Method of forming single-crystalline thin film by beam irradiator

ABSTRACT

In order to form a single-crystalline thin film on a polycrystalline substrate using plasma CVD, a downwardly directed mainly neutral Ne atom current is formed by an ECR ion generator (2). A reaction gas such as silane gas which is supplied from a reaction gas inlet pipe (13) is sprayed onto an SiO 2  substrate (11) by an action of the Ne atom current, so that an amorphous Si thin film is grown on the substrate (11) by a plasma CVD reaction. At the same time, a part of the Ne atom current having high directivity is directly incident upon the substrate (11), while another part thereof is incident upon the substrate (11) after its course is bent by a reflector (12). The reflector (12) is so set that all directions of the parts of the Ne atom current which are incident upon the substrate (11) are perpendicular to densest planes of single-crystalline Si. Therefore, the as-grown amorphous Si is sequentially converted to a single-crystalline Si thin film having crystal axes which are so regulated that the densest planes are oriented perpendicularly to the respective directions of incidence, by an action of the law of Bravais. Thus, a single-crystalline thin film is formed on a polycrystalline substrate.

This application is a continuation of application Ser. No. 08/597,097,filed on Feb. 7, 1996, now abandoned which is a Division of applicationSer. No. 08/239,969, filed on May 9, 1994, abandoned for FWC Ser. No.08/601,154, filed Feb. 13, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus forforming a single-crystalline thin film on a substrate, i.e., anarbitrary medium, and it relates to a method of and an apparatus forforming a single-crystalline thin film, which implement selective andefficient formation of a single-crystalline thin film, and it alsorelates to a beam irradiator, a beam irradiating method, and a beamreflecting device for enabling efficient formation of asingle-crystalline thin film or an axially oriented polycrystalline thinfilm on a substrate.

2. Background of the Invention

Plasma chemical vapor deposition (plasma CVD) is a sort of chemicalvapor deposition process (CVD), which is adapted to bring a reaction gasinto a plasma state for forming active radicals and ions and to cause achemical reaction under active environment, thereby forming a thin filmof a prescribed material on a substrate under a relatively lowtemperature. The plasma CVD, which can form various types of films underlow temperatures, has such advantages that it is possible to form anamorphous film while preventing crystallization, to employ anon-heat-resistant substrate such as a plastic substrate, and to preventthe as-formed film from a reaction with the substrate. Therefore, theapplication range of the plasma CVD is increasingly widened particularlyin relation to semiconductor industry.

It is possible to epitaxially form a single-crystalline thin film of aprescribed material on a single-crystalline substrate by carrying outthe plasma CVD under a temperature facilitating crystallization.

Generally, in order to form a single-crystalline thin film of aprescribed material on a single-crystalline substrate of the samematerial having the same crystal orientation, it is possible to employan epitaxial growth process. In the epitaxial growth process, however,it is impossible to form a single-crystalline thin film on apolycrystalline substrate or an amorphous substrate. Therefore, in orderto form a single-crystalline thin film on a substrate having a differentcrystal structure such as an amorphous substrate or a polycrystallinesubstrate, or a substrate of a different material, an amorphous thinfilm or a polycrystalline thin film is temporarily formed on thesubstrate so that the same is thereafter converted to asingle-crystalline thin film.

In general, a polycrystalline or amorphous semiconductor thin film issingle-crystallized by fusion recrystallization or lateral solid phaseepitaxy.

However, such a process has the following problems: In the fusionrecrystallization, the substrate is extremely thermally distorted whenthe thin film is prepared from a material having a high melting point,to damage physical and electrical properties of the thin film asemployed. Further, an electron beam or a laser beam is employed forfusing the thin film. Therefore, it is necessary to scan spots of theelectron beam or the laser beam along the overall surface of thesubstrate, and hence a long time and a high cost are required forrecrystallization.

On the other hand, the lateral solid phase epitaxy is easily influencedby a method of crystallizing the material forming the substrate, whilethe growth rate is disadvantageously slow in this process. In order togrow a single-crystalline thin film over a distance of about 10 μm, forexample, this process requires at least 10 hours. Further, it isdifficult to obtain a large crystal grain since a lattice defect iscaused to stop growth of the single crystal upon progress of the growthto some extent.

In each process, further, it is necessary to bring a seed crystal intocontact with the polycrystalline or amorphous thin film. In addition,the single crystal is grown in a direction along the major surface ofthe thin film, i.e., in a lateral direction, whereby the distance ofgrowth to the crystal is so increased that various hindrances take placeduring the growth of the single crystal. When the substrate is made ofan amorphous material such as glass, for example, the substrate has noregularity in lattice position and this irregularity influences ongrowth of the single crystal to disadvantageously result in growth of apolycrystalline film having large crystal grain sizes. In addition, itis difficult to selectively form a single-crystalline thin film having aprescribed crystal orientation on an arbitrary region of the substrate,due to the lateral growth.

In order to solve the aforementioned problems of the prior art, therehas been made an attempt for reducing the growth distance by utilizingvertical growth of the thin film, thereby reducing the growth time. Inother words, there has been tried a method of bringing a seed crystalinto contact with the overall surface of a polycrystalline or amorphousthin film for making solid phase epitaxial growth in a directionperpendicular to the major surface of the thin film, i.e., in thevertical direction. As the result, however, the seed crystal was merelypartially in contact with the amorphous thin film or the like and it wasimpossible to form a single-crystalline thin film by the as-expectedvertical solid phase epitaxial growth, since only lateral epitaxialgrowth was caused from the contact portion. According to this method,further, the seed crystal adhered to the as-grown single-crystallinefilm and it was extremely difficult to separate the former from thelatter, such that the as-grown thin film was disadvantageously separatedfrom the substrate following the seed crystal. Further, it is impossiblein practice to selectively form a single-crystalline thin film having aprescribed crystal orientation on an arbitrary region of the substrate,since it is necessary to accurately arrange a seed crystal of aprescribed shape on a prescribed position.

When the substrate itself has a single-crystalline structure, it isimpossible to form a single-crystalline thin film having a crystalorientation which is different from that of the substrate on thesubstrate by any conventional means.

This also applies to a polycrystalline thin film having single crystalaxes which are regulated along the same direction between crystalgrains, i.e., an axially oriented polycrystalline thin film. In otherwords, it is difficult to form an axially oriented polycrystalline thinfilm which is oriented in a desired direction on an arbitrary substrateby the prior art.

SUMMARY OF THE INVENTION

The inventor has found that, when a physical seed crystal is employed invertical growth of solid phase epitaxy, it is difficult to separate asingle-crystalline thin film as grown from the seed crystal due toadhesion therebetween, and that this problem can be solved when avirtual seed crystal of a large area is employed in place of thephysical seed crystal to obtain a virtual seed crystal for attaining thesame effect as a seed crystal adhering to the overall surface of asingle crystal in an excellent state with no physical adhesion on thesurface of the single crystal in termination of the crystal growth. Thepresent invention is based on this basic idea.

According to the present invention, a method of forming asingle-crystalline thin film is adapted to form a single-crystallinethin film of a prescribed material on a substrate by previously formingan amorphous thin film or a polycrystalline thin film of the prescribedmaterial on the substrate and irradiating the amorphous thin film or thepolycrystalline thin film with beams of neutral atoms or neutralmolecules of low energy levels causing no sputtering of the prescribedmaterial under a high temperature of not more than a crystallizationtemperature of the prescribed material from directions which areperpendicular to a plurality of densest crystal planes, having differentdirections, in the single-crystalline thin film to be formed.

The thin film is at a high temperature below a crystallizationtemperature, whereby the single crystal which is formed in the vicinityof the surface serves as a seed crystal, so that a single crystal isgrown toward a deep portion by vertical solid phase epitaxial growth tosingle-crystallize the overall region of the thin film along itsthickness. When the thin film is at a temperature exceeding thecrystallization temperature, the as-formed single crystal is convertedto a polycrystalline structure which is in a thermal equilibrium state.On the other hand, no crystallization toward a deep portion progressesat a temperature which is extremely lower than the crystallizationtemperature. Therefore, the temperature of the thin film is adjusted tobe at a high level below the crystallization temperature, such as alevel immediately under the crystallization temperature.

The seed crystal, which is formed by conversion from the amorphous thinfilm or the polycrystalline thin film, is integral with an amorphousthin film or the polycrystalline layer remaining in the deep portion.Namely, this layer is completely in contact with the seed crystal.Therefore, vertical solid phase epitaxial growth progresses in anexcellent state. Further, the seed crystal and the single crystal formedby solid epitaxial growth are made of the same material having the samecrystal orientation, whereby it is not necessary to remove the seedcrystal after formation of the single-crystalline thin film. Further,the single-crystalline thin film, which is formed by vertical solidphase epitaxial growth, can be efficiently obtained in a desired statein a short time.

In the method according to the present invention, it is possible to forma single-crystalline thin film on a substrate including apolycrystalline substrate or an amorphous substrate, while it is notnecessary to increase the temperature of the substrate to an extremelyhigh level. Therefore, it is possible to easily obtain asingle-crystalline thin film such as a wide-use semiconductor thin filmwhich is applied to a thin film transistor of liquid crystal display ora single-crystalline thin film which is applied to a three-dimensionalLSI. While a well-known metal evaporation film is inferior in qualitydue to a number of vacancies such that a migration phenomenon takesplace to easily cause disconnection when the same is applied tointerconnection of an electronic circuit, it is possible to prevent sucha problem according to the present invention.

Preferably, the atomic weights of atoms forming the beams are lower thanthe maximum one of the atomic weights of elements forming the prescribedmaterial.

The atomic weights of atoms forming the beams which are applied to thethin film or atoms forming molecules are lower than the maximum one ofthe atomic weights of elements forming the thin film, whereby most partsof the atoms forming the as-applied beams are rearwardly scattered onthe surface of the thin film or in the vicinity thereof, to hardlyremain in the thin film. Thus, electronic/physical properties of thethin film are hardly changed by residual of such atoms in thesingle-crystalline thin film.

Preferably, the beams are obtained by a single electron cyclotronresonance type ion generation source and a reflector which is arrangedin a path between the ion generation source and the amorphous thin filmor the polycrystalline thin film.

The beams which are applied to the thin film are obtained by a singlebeam source and a reflector which is arranged in a path, whereby it ispossible to irradiated the substrate with the beams from a plurality ofprescribed directions which are different from each other with norequirement for a plurality of beam sources. Namely, only a single beamsource having a complicated structure is sufficient in the methodaccording to the present invention, whereby a single-crystalline thinfilm can be formed with a simple apparatus structure. Since only onebeam source is sufficient, it is possible to form the thin film under ahigh vacuum. Further, the beam source is formed by an electron cyclotronresonance type ion generation source, whereby the ion beams have highdirectivity and it is possible to obtain strong neutral beams havingexcellent directivity at positions beyond prescribed distances from theion source with no means for neutralizing ions.

In the method according to the present invention, an amorphous thin filmor a polycrystalline thin film which is previously formed on a substratesurface is irradiated with beams of atoms or molecules from a pluralityof directions. The beams are at energy levels causing no sputtering onthe material as irradiated, whereby the law of Bravais acts such that alayer close to the surface of the amorphous thin film or thepolycrystalline thin film is converted to a crystal having such acrystal orientation that planes perpendicular to the directionsirradiated with the beams define densest crystal planes. The pluralityof beams are applied from directions perpendicular to a plurality ofdensest crystal planes having different directions, whereby theorientation of the as-formed crystal is set in a single one. In otherwords, a single-crystalline thin film having a regulated crystalorientation is formed in the vicinity of a surface of the amorphous thinfilm or the polycrystalline thin film.

The inventor has also found that a single-crystalline thin film can beobtained by growing a thin film and converting the same to asingle-crystalline simultaneously instead of previously forming a thinfilm. This invention is also based on this idea.

According to the present invention, a method of forming asingle-crystalline thin film forms a single-crystalline thin film of aprescribed material on a polycrystalline substrate or an amorphoussubstrate using plasma chemical vapor deposition by supplying a reactiongas onto the substrate under a low temperature allowing nocrystallization of the prescribed material with the plasma chemicalvapor deposition alone while simultaneously irradiating the substratewith beams of a low energy gas causing no sputtering of the prescribedmaterial from directions which are perpendicular to a plurality ofdensest crystal planes having different directions in thesingle-crystalline thin film to be formed.

In the method according to the present invention, a thin film of aprescribed material is formed on a substrate by plasma chemical vapordeposition, while the substrate is irradiated with beams of a gas from aplurality of directions. The gas beams are at energy levels causing nosputtering on the material as irradiated, whereby the law of Bravaisacts such that the thin film of the prescribed material as being formedis sequentially converted to a crystal in such a crystal orientationthat planes perpendicular to directions of the beams define densestcrystal planes. The substrate is irradiated with a plurality of gasbeams from directions perpendicular to a plurality of densest crystalplanes having different directions, whereby the as-formed crystal hasonly one orientation. In other words, a single-crystalline thin filmhaving a regulated crystal orientation is formed.

Under a temperature facilitating crystallization of a prescribedmaterial by plasma chemical vapor deposition alone with no beamirradiation, crystal orientations are arbitrarily directed regardless ofdirections of beam irradiation and cannot be regulated, while apolycrystalline film is formed. Therefore, temperature control isperformed to a low level for facilitating no crystallization with plasmachemical vapor deposition alone.

In the method according to the present invention, further, conversion toa single crystal simultaneously sequentially progresses in the processof growth of the thin film by plasma chemical vapor deposition. Thus, itis possible to form a single-crystalline thin film having a largethickness under a low temperature.

Preferably, the gas is an inert gas.

The substrate is irradiated with an inert gas, whereby atoms or ionswhich may remain in the as-formed thin film after irradiation exert nobad influence on electronic/physical properties of thesingle-crystalline thin film as impurities.

Preferably, the atomic weight of an element forming the inert gas islower than the maximum one of the atomic weights of elements forming theprescribed material.

The atomic weight of an element forming the inert gas is lower than themaximum atomic weight of elements forming the prescribed material whichis grown as a thin film, whereby most parts of atoms or ions of theas-applied inert gas rearwardly recoil on the surface of the thin filmor in the vicinity thereof, to hardly remain in the thin film.

Preferably, the prescribed material contains an element forming a gasmaterial which is in a gas state under ordinary temperatures, and thebeams of the gas are those of the gas material.

The gas as applied contains elements forming the material which is grownas the thin film. Even if atoms or ions of the elements remain afterirradiation, therefore, the same exert no bad influence on the as-formedsingle-crystalline thin film as impurities. Further, it is also possibleto supply the element to the thin film only by application of the gasbeams without introducing the same into the reaction gas.

Preferably, the reaction gas contains a reaction gas material which isformed by an impurity element to be added to the prescribed material.

The reaction gas contains an impurity element to be added to thematerial which is grown as the thin film, whereby it is possible to forma p-type or n-type semiconductor single-crystalline thin film information of a semiconductor single-crystalline thin film, for example.In other words, it is possible to form a single-crystalline thin filmcontaining a desired impurity.

Preferably, a plurality of types of impurity elements are so employedthat a plurality of types of reaction gas materials which are formed byrespective ones of the plurality of types of impurity elements arealternately supplied onto the substrate.

A plurality of types of reaction gas materials formed by respective onesof a plurality of types of impurity elements are alternately suppliedonto the substrate, whereby it is possible to form a single-crystallinethin film having a plurality of types of single-crystalline layerscontaining the respective ones of the plurality of types of impuritiessuch that an n-type semiconductor single-crystalline layer is formed ona p-type semiconductor single-crystalline layer in formation of asemiconductor single-crystalline thin film, for example.

Preferably, the beams of the gas are obtained by a single beam sourceand a reflector which is arranged in a path between the beam source andthe substrate.

The beams of the gas which are applied to the substrate are obtained bya single beam source and a reflector which is arranged on a path,whereby it is possible to irradiate the substrate with the gas beamsfrom directions which are perpendicular to a plurality of densestcrystal planes having different directions with no requirement for aplurality of beam sources. In other words, only a single beam sourcehaving a complicated structure may be so prepared that it is possible toform the single-crystalline thin film with a simple structure in themethod according to the present invention. Since a single beam sourcemay be sufficient, further, it is possible to form the thin film under ahigh vacuum.

Preferably, the beam source is an ion generation source generating anion beam of the gas, and the reflector is a metal reflector which issubstantially made of a metal.

The beam source has an ion generation source which generates an ion beamof the gas, and the reflector is prepared from a metal reflector whichis substantially made of a metal. Therefore, the ion beam of the gasgenerated from the ion source is converted to a neutral beam when thesame is reflected by the metal reflector. Therefore, the substrate isirradiated with parallel beams which are regulated in direction.Further, it is possible to prepare the substrate from an electricalinsulating substrate.

Preferably, the beam source is an electron cyclotron resonance type iongeneration source.

The beam source is formed by an electron cyclotron resonance type iongeneration source. Therefore, the ion beam has high directivity, whileit is possible to obtain a strong neutral beam in a portion which isseparated beyond a prescribed distance from the ion source with noemployment of means for neutralizing ions. It is possible to irradiatethe substrate with parallel beams from a plurality of prescribeddirections by reflecting the neutral beam by the reflector and applyingthe same to the substrate. Further, it is also possible to prepare thesubstrate from an electrical insulating substrate.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material comprises (a) astep of forming an amorphous or polycrystalline thin film of theprescribed material on a substrate, (b) a step of forming a maskingmaterial on the thin film, (c) a step of selectively removing themasking material, and (d) a step of irradiating the substrate with gasbeams of low energy levels causing no sputtering of the prescribedmaterial from directions which are perpendicular to a plurality ofdensest crystal planes having different directions in thesingle-crystalline thin film to be formed while utilizing theselectively removed masking material as a screen under a hightemperature below the crystallization temperature of the prescribedmaterial.

Preferably, the steps (b) to (d) are carried out plural times whilevarying directions for applying the beams in the step (d), therebyselectively converting the thin film to a single crystal having aplurality of types of crystal orientations.

In the method according to the present invention, the amorphous orpolycrystalline thin film which is previously formed on the substrate isirradiated with gas beams from a plurality of directions. These beamsare at energy levels causing no sputtering on the material asirradiated, whereby the law of Bravais acts so that a layer which is inthe vicinity of the surface of the as-irradiated thin film is convertedto a crystal having such a crystal orientation that planes perpendicularto the directions of the beams define densest crystal planes. Theplurality of gas beams are applied from directions which areperpendicular to a plurality of densest crystal planes having differentdirections, whereby the as-formed crystal is set in a singleorientation. Namely, a single-crystalline layer having a regulatedcrystal orientation is formed in the vicinity of the surface of thepolycrystalline thin film. Further, a masking material is formed on thethin film to be irradiated in advance of irradiation, and this maskingmaterial is selectively removed. Thus, irradiation progresses withlimitation on a specific region of the substrate corresponding to theselectively removed portion of the masking material, whereby thesingle-crystalline layer is formed only in the vicinity of the surfaceportion of the thin film corresponding to the specific region.

Further, the thin film is at a high temperature below thecrystallization temperature and hence the single crystal which is formedin the vicinity of its surface serves as a seed crystal to be growntoward a deep portion by vertical solid phase epitaxial growth, wherebythe overall region of the as-irradiated thin film is single-crystallizedalong the thickness. If the thin film is at a temperature exceeding thecrystallization temperature, the as-formed single crystal is convertedto a polycrystalline structure which is in a thermal equilibrium state.On the other hand, no crystallization toward a deep portion progressesat a temperature which is extremely lower than the crystallizationtemperature. Therefore, the temperature of the thin film is adjusted tobe at a high level below the crystallization temperature, such as alevel immediately under the crystallization temperature, for example.

According to the inventive method, as hereinabove described, it ispossible to selectively form a single-crystalline thin film having aregulated crystal orientation on an arbitrary specific region of asubstrate.

In the method according to the present invention, the steps fromformation of the masking material to irradiation with the gas beams arerepeated while varying directions of irradiation. Therefore, it ispossible to selectively form single-crystalline thin films havingdifferent crystal orientations on a plurality of arbitrary specificregions of the substrate.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material comprises (a) astep of forming an amorphous or polycrystalline thin film of theprescribed material on a substrate, (b) a step of forming a maskingmaterial on the thin film, (c) a step of selectively removing themasking material, (d) a step of etching the thin film while utilizingthe selectively removed masking material as a screen, therebyselectively removing the thin film while leaving a specific region onthe substrate, and (e) a step of irradiating the substrate with gasbeams of low energy levels causing no sputtering of the prescribedmaterial from directions which are perpendicular to a plurality ofdensest crystal planes having different directions in thesingle-crystalline thin film to be formed under a high temperature belowthe crystallization temperature of the prescribed material.

In the method according to the present invention, the amorphous orpolycrystalline thin film is selectively removed while leaving aspecific region on the substrate and thereafter the thin film isirradiated with gas beams under a prescribed temperature to facilitateaction of the law of Bravais and vertical solid phase epitaxial growth,thereby converting the thin film to a single-crystalline thin film.Thus, it is possible to selectively form a single-crystalline thin filmhaving a regulated crystal orientation on an arbitrary specific regionof the substrate.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material comprises (a) astep of forming an amorphous or polycrystalline thin film of theprescribed material on a substrate, (b) a step of irradiating thesubstrate with gas beams of low energy levels causing no sputtering ofthe prescribed material from directions which are perpendicular to aplurality of densest crystal planes having different directions in thesingle-crystalline thin film to be formed under a high temperature belowthe crystallization temperature of the prescribed material, (c) a stepof forming a masking material on the thin film after the step (b), (d) astep of selectively removing the masking material, and (e) a step ofetching the thin film while utilizing the selectively removed maskingmaterial as a screen, thereby selectively removing the thin film.

In the method according to the present invention, the amorphous orpolycrystalline thin film formed on the substrate is irradiated with gasbeams under a prescribed temperature to facilitate action of the law ofBravais and vertical solid phase epitaxial growth, thereby convertingthe thin film to a single-crystalline thin film. Thereafter thesingle-crystalline thin film is selectively removed while leaving aspecific region on the substrate. Therefore, it is possible toselectively form a single-crystalline thin film having a regulatedcrystal orientation on an arbitrary specific region on the substrate.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material comprises (a) astep of forming an amorphous or polycrystalline thin film of theprescribed material on a substrate, (b) a step of irradiating thesubstrate with gas beams of low energy levels causing no sputtering ofthe prescribed material from directions which are perpendicular to aplurality of densest crystal planes having different directions in thesingle-crystalline thin film to be formed under a low temperaturecausing no crystallization of the prescribed material by the step (a)alone while carrying out the step (a), (c) a step of forming a maskingmaterial on the thin film after the steps (a) and (b), (d) a step ofselectively removing the masking material, and (e) a step of etching thethin film while utilizing the selectively removed masking material as ascreen, thereby selectively removing the thin film.

In the method according to the present invention, an amorphous orpolycrystalline thin film is formed on the substrate with application ofgas beams under a prescribed temperature for facilitating action of thelaw of Bravais, thereby converting the thin film as being formedsequentially to a single-crystalline thin film. Thereafter thesingle-crystalline thin film is selectively removed while leaving aspecific region on the substrate. Thus, it is possible to selectivelyform a single-crystalline thin film having a regulated crystalorientation on an arbitrary specific region of the substrate.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material comprises (a) astep of forming an amorphous or polycrystalline thin film of theprescribed material on a substrate, (b) a step of irradiating thesubstrate with gas beams of low energy levels causing no sputtering ofthe prescribed material from directions which are perpendicular to aplurality of densest crystal planes having different directions in thesingle-crystalline thin film to be formed under a high temperature belowthe crystallization temperature of the prescribed material, (c) a stepof forming a masking material on the thin film after the step (b), (d) astep of selectively removing the masking material, and (e) a step ofirradiating the substrate with the gas beams of low energy levelscausing no sputtering of the prescribed material from directions whichare perpendicular to the plurality of densest crystal planes havingdifferent directions in the single-crystalline thin film to be formedand different from those in the step (b), while utilizing theselectively removed masking material as a screen.

In the method according to the present invention, the amorphous orpolycrystalline thin film formed on the substrate is irradiated with gasbeams under a prescribed temperature to facilitate action of the law ofBravais and vertical solid phase epitaxial growth, thereby convertingthe thin film to a single-crystalline thin film. Thereafter a maskingmaterial is selectively formed on this single-crystalline thin film,which in turn is again irradiated with gas beams from new directions. Atthis time, the masking material serves as a screen for the gas beams,whereby the single-crystalline thin film is converted to a secondsingle-crystalline thin film having a new crystal orientation on aregion where the masking material is selectively removed. Namely, it ispossible to selectively form single-crystalline thin films havingdifferent crystal orientations on a plurality of arbitrary specificregions of the substrate.

The atomic weight of an element forming the gas is preferably lower thanthe maximum one of the atomic weights of elements forming the prescribedmaterial.

The atomic weight of the element forming the gas beams which are appliedonto the substrate is lower than the maximum one of the atomic weightsof the elements forming the thin film as irradiated, whereby most partsof the atoms forming the applied gas are rearwardly scattered on thesurface of the thin film as irradiated or in the vicinity thereof, tohardly remain in the thin film. Thus, it is possible to obtain asingle-crystalline thin film having a small amount of impurities.

The atomic weight of an element forming the gas is preferably lower thanthe maximum one of the atomic weights of elements forming the maskingmaterial.

The atomic weight of the element forming the gas beams which are appliedonto the substrate is lower than the maximum one of the atomic weightsof the elements forming the masking material, whereby most parts of theatoms forming the gas as applied are rearwardly scattered on the surfaceof the masking material or in the vicinity thereof, to hardly penetrateinto the masking material and the thin film as irradiated. Thus, it ispossible to obtain a single-crystalline thin film having a small amountof impurities.

The present invention is also directed to an apparatus for forming asingle-crystalline thin film. According to the present invention, anapparatus for forming a single-crystalline thin film of a prescribedmaterial on a substrate comprises irradiation means for irradiating thesubstrate with gas beams of low energy levels causing no sputtering ofthe prescribed material from directions which are perpendicular to aplurality of densest crystal planes having different directions in thesingle-crystalline thin film to be formed, and substrate moving meansfor making the substrate scanned with respect to the irradiation means.

Preferably, the apparatus for forming a single-crystalline thin filmfurther comprises beam focusing means for bringing sections of the gasbeams into strip shapes on the substrate.

In the apparatus according to the present invention, the substrate canbe scanned by the substrate moving means, whereby it is possible to forma single-crystalline thin film having high homogeneity on a longsubstrate.

Further, the apparatus according to the present invention comprises beamfocusing means for bringing sections of the gas beams into strip shapeson the substrate, whereby it is possible to efficiently form asingle-crystalline thin film with higher homogeneity by scanning thesubstrate.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises a single beam source for supplying a beam of a gas, areflector for reflecting at least a part of the beam which is suppliedby the beam source, thereby implementing irradiation of the substratewith the gas in a plurality of prescribed directions of incidence, andreflector driving means for varying the angle of inclination of thereflector.

In the apparatus according to the present invention, the gas beams to beapplied to the thin film are obtained by a single beam source and areflector which is arranged in a path, whereby it is possible toirradiate the thin film with the gas beams from a plurality ofprescribed directions which are different to each other with norequirement for a plurality of beam sources. Further, this apparatuscomprises reflector driving means, whereby it is possible to change andre-set directions of incidence of the beams upon the substrate. Thus, itis possible to form a plurality of types of single-crystalline thinfilms having different crystal structures or different crystalorientations by a single apparatus.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises a single beam source for supplying a beam of a gas, aplurality of reflectors, each of which reflects at least a part of thebeam supplied by the beam source, thereby implementing irradiation ofthe substrate with the gas in a plurality of prescribed directions ofincidence related to the angle of inclination of the reflector, andreflector exchange means for selecting a prescribed one from theplurality of reflectors and utilizing the same for reflecting the beam.

In the apparatus according to the present invention, the gas beams to beapplied to the thin film are obtained by a single beam source and areflector which is arranged in a path, whereby it is possible toirradiate the thin film with the gas beams from a plurality ofprescribed directions which are different from each other with norequirement for a plurality of beam sources. Further, this apparatuscomprises reflector exchange means, whereby it is possible toarbitrarily select directions of incidence of the beams upon thesubstrate from a plurality of reflectors to re-set the same. Thus, it ispossible to form a plurality of types of single-crystalline thin filmshaving different crystal structures or crystal orientations by a singleapparatus.

The apparatus for forming a single-crystalline thin film preferablyfurther comprises film forming means for forming an amorphous orpolycrystalline thin film of the same material as the single-crystallinethin film on the substrate.

The apparatus of the present invention comprises film forming means suchas chemical vapor deposition means, for example, whereby it is possibleto sequentially convert the thin film as being formed to asingle-crystalline thin film by forming the thin film while irradiatingthe same with gas beams. Thus, there is no need to facilitate verticalepitaxial growth of the thin film, whereby the single-crystalline thinfilm can be formed under a low temperature.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises etching means for etching a surface of the substrate, filmforming means for forming an amorphous or polycrystalline thin film ofthe prescribed material on the surface of the substrate, and irradiationmeans for irradiating the substrate with gas beams of low energy levelscausing no sputtering of the prescribed material from directions whichare perpendicular to a plurality of densest crystal planes havingdifferent directions in the single-crystalline thin film to be formed.Treatment chambers provided in the aforementioned means for storing thesubstrate communicate with each other. The apparatus further comprisessubstrate carrying means for introducing and discharging the substrateinto and from the respective treatment chambers.

The apparatus according to the present invention comprises etchingmeans, film forming means and irradiation means having treatmentchambers communicating with each other, whereby it is possible to startfilm formation by carrying out etching treatment for removing an oxidefilm and preventing new progress of oxidation before forming the thinfilm on the substrate by employing this apparatus. Further, thisapparatus comprises substrate carrying means, whereby the substrate canbe efficiently carried into the respective treatment chambers.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratehaving a single-crystalline structure comprises irradiation means forirradiating the substrate with gas beams of low energy levels causing nosputtering of the prescribed material from directions which areperpendicular to a plurality of densest crystal planes having differentdirections in the single-crystalline thin film to be formed, andattitude control means for controlling the attitude of the substrate forsetting prescribed relations between directions of crystal axes of thesubstrate and directions of incidence of the beams.

The apparatus according to the tenth aspect of the present inventioncomprises attitude control means, whereby it is possible to setprescribed relations between the crystal axes of the single-crystallinesubstrate and the directions of incidence of the gas beams by employingthis apparatus. Thus, it is possible to epitaxially form a newsingle-crystalline thin film on a single-crystalline substrate at atemperature below the crystallization temperature.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises film forming means for forming an amorphous or polycrystallinethin film of the prescribed material on the substrate by supplying areaction gas, irradiation means for irradiating the substrate with gasbeams of low energy levels causing no sputtering of the prescribedmaterial from directions which are perpendicular to a plurality ofdensest crystal planes having different directions in thesingle-crystalline thin film to be formed, and substrate rotating meansfor rotating the substrate.

The apparatus according to the present invention comprises substraterotating means, whereby it is possible to facilitate formation of anamorphous or polycrystalline thin film by intermittently applying thebeams while regularly supplying the reaction gas and rotating thesubstrate during application pauses. Thus, it is possible to form anamorphous or polycrystalline thin film having high homogeneity, wherebyhigh homogeneity is also attained in a single-crystalline thin filmwhich is obtained by converting the same.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises film forming means for forming an amorphous or polycrystallinethin film of the prescribed material on the substrate by supplying areaction gas, and irradiation means for irradiating the substrate withgas beams of low energy levels causing no sputtering of the prescribedmaterial from directions which are perpendicular to a plurality ofdensest crystal planes having different directions in thesingle-crystalline thin film to be formed. The film forming means hassupply system rotating means for rotating an end portion of a supplypath for supplying the substrate with the reaction gas with respect tothe substrate.

The apparatus according to the present invention comprises supply systemrotating means, whereby it is possible to obtain a single-crystallinethin film having high homogeneity while regularly supplying the reactiongas and applying the beams with no intermittent application of thebeams. Namely, it is possible to efficiently form a single-crystallinethin film having high homogeneity.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises a plurality of irradiation means for irradiating the substratewith a plurality of gas beams of low energy levels causing no sputteringof the prescribed material from directions which are perpendicular to aplurality of densest crystal planes having different directions in thesingle-crystalline thin film to be formed respectively, and controlmeans for independently controlling operating conditions in theplurality of irradiation means respectively.

In the apparatus according to the present invention, control meansindependently controls operating conditions in irradiation means such asoutput beam densities, for example, whereby states of a plurality ofbeams which are applied to the substrate are optimumly controlled. Thus,it is possible to efficiently form a high-quality single-crystallinethin film.

The irradiation means preferably comprises an electron cyclotronresonance type ion source, and the gas beams are supplied by the ionsource.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises irradiation means for irradiating the substrate with beams ofa gas supplied by an ion source at low energy levels causing nosputtering of the prescribed material from directions which areperpendicular to a plurality of densest crystal planes having differentdirections in the single-crystalline thin film to be formed, and biasmeans for applying a bias voltage across the ion source and thesubstrate in a direction for accelerating ions.

In the apparatus according to the present invention, bias means appliesa bias voltage across the ion source and the substrate, whereby the gasbeams are improved in directivity. Thus, it is possible to form ahigh-quality single-crystalline thin film having high homogeneity of thecrystal orientation.

According to the present invention, an apparatus for forming asingle-crystalline thin film of a prescribed material on a substratecomprises irradiation means for irradiating the substrate with beams ofa gas supplied by an ion source at low energy levels causing nosputtering of the prescribed material from directions which areperpendicular to a plurality of densest crystal planes having differentdirections in the single-crystalline thin film to be formed, with a gridwhich is provided in the vicinity of an ion outlet of the ion source,and grid voltage applying means for applying a voltage to the grid forcontrolling conditions for extracting ions from the ion source.

In the apparatus according to the present invention, grid voltageapplying means optimumly controls conditions for extracting ions fromthe ion source, whereby it is possible to efficiently form ahigh-quality single-crystalline thin film.

In the apparatus according to the present invention, the beam source ispreferably an electron cyclotron resonance type ion source.

In the apparatus according to the present invention, the gas beams aresupplied by an electron cyclotron resonance type ion source, whereby theion beams are excellent in directivity while it is possible to obtainstrong neutral beams having excellent directivity at positions beyond aprescribed distance from the ion source without employing means forneutralizing ions.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a container forstoring the sample, and a beam source for irradiating the target surfaceof the sample which is set in a prescribed position of the containerwith the gas beam, and at least a surface of a portion irradiated withthe beam is made of a material having threshold energy which is higherthan energy of the beam in sputtering by irradiation with the beam amongan inner wall of the container and a member which is stored in thecontainer.

At least the surface of the portion irradiated with the beam is made ofa material having threshold energy which is higher than energy of thebeam in sputtering by the irradiation with the beam among the inner wallof the container and the member stored in the container, whereby nosputtering is caused even if the beam reaches the member. Therefore,consumption of the member by sputtering is suppressed, whilecontamination of the target sample with the material element forming themember is prevented.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a container forstoring the sample, and a beam source for irradiating the target surfaceof the sample which is set in a prescribed position of the containerwith the gas beam, and at least a surface of a portion irradiated withthe beam is made of a material having threshold energy with respect tosputtering which is higher than that in the target surface of the sampleamong an inner wall of the container and a member which is stored in thecontainer.

At least the surface of the portion irradiated with the beam is made ofa material having threshold energy with respect to sputtering which ishigher than that in the target surface of the sample among the innerwall of the container and the member stored in the container, whereby nosputtering is caused in this member when the target surface of thesample is irradiated with the beam causing no sputtering. Therefore,consumption of the member by sputtering is suppressed under such usage,while contamination of the target sample with the material elementforming the member is prevented.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a container forstoring the sample, and a beam source for irradiating the target surfaceof the sample which is set in a prescribed position of the containerwith the gas beam, and at least a surface of a portion irradiated withthe beam is made of a material containing an element which is larger inatomic weight than that forming the gas among an inner wall of thecontainer and a member which is stored in the container.

At least the surface of the portion irradiated with the beam is made ofa material containing an element which is larger in atomic weight thanthat forming the beam gas among the inner wall of the container and themember stored in the container, whereby permeation of a differentelement in the member is suppressed. Therefore, deterioration of themember caused by invasion of the different element is suppressed.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a container forstoring the sample, and a beam source for irradiating the target surfaceof the sample which is set in a prescribed position of the containerwith the gas beam, and at least a surface of a portion irradiated withthe beam is made of the same material as that forming the target surfaceof the sample among an inner wall of the container and a member which isstored in the container.

At least the surface of the portion irradiated with the beam is made ofthe same material as that forming the target surface of the sample amongthe inner wall of the container and the member stored in the container,whereby the target sample is not contaminated with the material elementforming the member even if sputtering is caused in this member.

The member stored in the container preferably includes reflecting meanswhich is interposed in a path of the beam for separating the beam into aplurality of components and irradiating the target surface of the samplewith the plurality of components from directions which are differentfrom each other.

The reflecting means is stored in the container and at least the surfaceof the portion irradiated with the beam is made of a material causing nosputtering, the same material as that of the target surface of thesample, or a material containing an element which is larger in atomicweight than that forming the beam gas, whereby contamination of thesample by sputtering of the reflecting means is prevented ordeterioration of the reflecting means is suppressed.

The present invention is also directed to a beam irradiating method.According to the present invention, a beam irradiating method ofirradiating a target surface of a sample with a gas beam comprises astep of setting the sample in a prescribed position of a container, anda step of irradiating the target surface of the sample which is set inthe container with the gas beam, and the target surface is irradiatedwith the beam at energy which is lower than threshold energy ofsputtering in a surface of a portion which is irradiated with the beamamong an inner wall of the container and a member stored in thecontainer.

The target surface is irradiated with the beam at energy which is lowerthan threshold energy of sputtering on the surface of the portionirradiated with the beam among the inner wall of the container and themember stored in the container, whereby no sputtering is caused even ifthe beam reaches the member. Therefore, consumption of the member bysputtering is suppressed, while contamination of the target sample withthe material element forming the member is prevented.

The present invention is also directed to a method of formingsingle-crystalline thin film. According to the present invention, amethod of forming a single-crystalline thin film of a prescribedmaterial on a substrate comprises a step of depositing the prescribedmaterial on the substrate under a low temperature causing nocrystallization of the prescribed material and irradiating theprescribed material as deposited with a gas beam of low energy causingno sputtering of the prescribed material from one direction, therebyforming an axially oriented polycrystalline thin film of the material,and a step of irradiating the axially oriented polycrystalline thin filmwith gas beams of low energy causing no sputtering of the prescribedmaterial under a high temperature below a crystallization temperature ofthe prescribed material from directions which are perpendicular to aplurality of densest crystal planes of different directions in thesingle-crystalline thin film, thereby converting the axially orientedpolycrystalline thin film to a single-crystalline thin film.

The axially oriented polycrystalline thin film is previously formed onthe substrate and thereafter irradiated with the beams from a pluralityof directions so that the thin film is converted to a single-crystallinethin film. Therefore, even if the substrate is not uniformly irradiatedwith the beams from the plurality of directions due to a screen formedon the substrate, for example, at least either a single-crystalline thinfilm or an axially oriented polycrystalline thin film is formed on anyportion on the substrate, whereby no remarkable deterioration ofcharacteristics is caused.

According to the present invention, a method of forming asingle-crystalline thin film of a prescribed material on a substratecomprises a step of depositing the prescribed material on the substratethereby forming a thin film of the material, a step of irradiating thethin film with a gas beam of low energy causing no sputtering of theprescribed material under a high temperature below a crystallizationtemperature of the prescribed material from one direction after thestep, thereby converting the thin film to an axially orientedpolycrystalline thin film, and a step of irradiating the axiallyoriented polycrystalline thin film with gas beams of low energy causingno sputtering of the prescribed material under a high temperature belowthe crystallization temperature of the prescribed material fromdirections which are perpendicular to a plurality of densest crystalplanes of different directions in the single-crystalline thin film,thereby converting the axially oriented polycrystalline thin film to asingle-crystalline thin film.

The axially oriented polycrystalline thin film is previously formed onthe substrate and thereafter irradiated with the beams from a pluralityof directions, so that the thin film is converted to asingle-crystalline thin film. Therefore, even if the substrate is notuniformly irradiated with the beams from the plurality of directions dueto a screen formed on the substrate, for example, at least either asingle-crystalline thin film or an axially oriented polycrystalline thinfilm is formed on any portion on the substrate, whereby no remarkabledeterioration of characteristics is caused.

The direction of the gas beam in formation of the axially orientedpolycrystalline thin film is preferably identical to one of theplurality of directions of the gas beams in the conversion of theaxially oriented polycrystalline thin film to the single-crystallinethin film.

The direction of application of the gas beam in formation of the axiallyoriented polycrystalline thin film is identical to one of the pluralityof directions of gas beams for converting the axially orientedpolycrystalline thin film to a single-crystalline thin film, wherebyconversion to the single-crystalline thin film is smoothly carried out.

The gas is preferably an inert gas.

The beam of an inert gas is so applied that no particularly remarkableinfluence is exerted on the electrophysical properties of the thin filmeven if the gas remains in the single-crystalline thin film as formed,while it is possible to easily remove the as-invaded gas from the thinfilm.

The atomic weight of an element forming the inert gas is preferablylower than the maximum atomic weight among those of elements forming theprescribed material.

The atomic weight of the element forming the inert gas is lower than themaximum atomic weight of elements forming the prescribed material whichis grown as the thin film, whereby most part of atoms or ions of theapplied inert gas are rearwardly scattered on the surface of the thinfilm or in the vicinity thereof, to hardly remain in the thin film.

The prescribed material preferably contains an element forming a gasmaterial which is a gas under a normal temperature, and the gas beam ispreferably a beam of the gas material.

The gas as applied contains an element forming the material grown as athin film. Even if atoms or ions of the element remain in the thin filmafter irradiation, therefore, these will not exert a bad influence onthe single-crystalline thin film as impurities.

The gas beam is preferably formed by an electron cyclotron resonance ionsource.

The beam generation source is an electron cyclotron resonance iongeneration source. Therefore, the ion beam has high directivity, while astrong neutral beam can be obtained at a distance exceeding a prescribedlength from the ion generation source without employing means forneutralizing ions. Further, it is possible to employ an electricallyinsulating substrate without employing means for neutralizing the ions.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a single beamsource for supplying the beam, and reflecting means for reflecting thebeam which is supplied by the beam source, thereby enabling irradiationof the target surface with the gas in a plurality of prescribeddirections of incidence, and the reflecting means comprises a reflectorhaving a plurality of reflecting surfaces for reflecting the beam in aplurality of directions, and a screen which is interposed in a path ofthe beam between the beam source and the reflecting surfaces forselectively passing the beam thereby preventing multiple reflection bythe plurality of reflecting surfaces.

Multiple reflection of the beam by the plurality of reflecting surfacesis prevented by the screen, whereby no beam is applied from a directionother than a prescribed direction of incidence.

The screen preferably further selectively passes the beam to uniformlyirradiate the target surface with the beam.

The target surface is uniformly irradiated with the beam by action ofthe screen. Therefore, a high quality single-crystalline thin film isformed when the apparatus is applied to formation of asingle-crystalline thin film, for example.

The present invention is also directed to a beam reflecting device.According to the present invention, a beam reflecting device forreflecting a gas beam which is supplied from a single beam sourcethereby enabling irradiation of a target surface of a sample with thegas in a plurality of prescribed directions of incidence comprises areflector having a plurality of reflecting surfaces for reflecting thebeam in a plurality of directions, and a screen which is interposed in apath of the beam between the beam source and the reflecting surfaces forselectively passing the beam thereby preventing multiple reflection bythe plurality of reflecting surfaces.

Multiple reflection of the beam by the plurality of reflecting surfacesis prevented by the screen, whereby no beam is applied from a directionother than a prescribed direction of incidence.

The screen preferably further selectively passes the beam to uniformlyirradiate the target surface with the beam.

The target surface is uniformly irradiated with the beam by action ofthe screen. Therefore, a high-quality single-crystalline thin film isformed when the apparatus is applied to formation of asingle-crystalline thin film, for example.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with a gas beam comprises a single beamsource for supplying the beam, and reflecting means for reflecting thebeam which is supplied by the beam source, thereby enabling irradiationof the target surface with the gas in a plurality of prescribeddirections of incidence, and the reflecting means comprises a firstreflector which is arranged in a path of the beam supplied from the beamsource for reflecting the beam in a plurality of directions therebygenerating a plurality of divergent beams having beam sections which aretwo-dimensionally enlarged with progress of the beams, and a secondreflector having a concave reflecting surface for further reflecting theplurality of divergent beams to be incident upon the target surfacesubstantially as parallel beams from a plurality of directions.

The gas beams applied to the target surface of the sample are obtainedby the single beam source and the reflecting means provided in the path,whereby it is possible to irradiate the target surface with gas beamsfrom a plurality of different prescribed directions with no requirementfor a plurality of beam sources. Further, the beam is reflected by thefirst reflector to be two-dimensionally diverged in a plurality ofdirections and then converted to substantially parallel beams by thesecond reflector, whereby the beam can be uniformly applied to thetarget surface which is wider than the section of the beam supplied fromthe beam source. Therefore, it is possible to widely and efficientlyform a single-crystalline thin film of a prescribed material on a widesubstrate provided with a thin film of the prescribed material on itssurface or a wide substrate having a thin film of the prescribedmaterial being grown on its surface without scanning the substrate, byirradiating the substrate with a gas beam by this apparatus.

The reflecting means preferably further comprises rectifying means whichis provided in a path of the beams between the first reflector and thesubstrate for regularizing directions of the beams.

The rectifying means is arranged in the path of the beam between thefirst reflector and the sample, whereby the beam can be regulated alonga prescribed direction. Therefore, no strict accuracy is required forthe shapes and arrangement of the respective reflectors, whereby theapparatus can be easily structured.

The reflecting means preferably further comprises beam distributionadjusting means which is interposed in a path of the beam between thebeam source and the first reflector for adjusting distribution of thebeam on a section which is perpendicular to the path, thereby adjustingthe amounts of respective beam components reflected by the firstreflector in the plurality of directions.

The beam distribution adjusting means adjusts the amounts of a pluralityof beam components reflected by the first reflector, whereby the amountsof a plurality of beam components which are incident upon the targetsurface from a plurality of directions can be adjusted. Therefore, theamounts of the respective beam components incident upon the substratecan be optimumly set to be identical to each other, for example, wherebyit is possible to efficiently form a high-quality single-crystallinethin film.

According to the present invention, a beam reflecting device forreflecting a gas beam which is supplied from a single beam sourcethereby enabling irradiation of a target surface of a sample with thegas in a plurality of prescribed directions of incidence comprises afirst reflector for reflecting the beam in a plurality of directionsthereby generating a plurality of divergent beams having beam sectionswhich are two-dimensionally enlarged with progress of the beams, and asecond reflector having a concave reflecting surface for furtherreflecting the plurality of divergent beams to be incident upon thetarget surface substantially as parallel beams from a plurality ofdirections.

The gas beam which is supplied from the single beam source is reflectedby the first reflector to be two-dimensionally diverged in a pluralityof directions and then converted to substantially parallel beams by thesecond reflector, whereby it is possible to irradiate the target surfacewhich is wider than the section of the beam supplied from the beamsource from a plurality of directions with no requirement for aplurality of beam sources. Therefore, it is possible to widely andefficiently form a single-crystalline thin film of a prescribed materialon a wide substrate provided with a thin film of the prescribed materialon its surface or a wide substrate having a thin film of the prescribedmaterial being grown on its surface without scanning the substrate, byirradiating the substrate with a gas beam by this apparatus.

According to the present invention, a beam irradiator for irradiating atarget surface of a sample with gas beams comprises a plurality of beamsources for supplying the gas beams, and a plurality of reflecting meansfor reflecting the beams which are supplied by the plurality of beamsources thereby enabling irradiation of a common region of the targetsurface with the gas in a plurality of prescribed directions ofincidence, and each reflecting means comprises a first reflector whichis arranged in a path of each beam supplied from each beam source forreflecting the beam thereby generating a beam having a beam sectionwhich is two-dimensionally enlarged with progress of the beam, and asecond reflector having a concave reflecting surface for furtherreflecting the divergent beam to be incident upon a linear orstrip-shaped common region of the target surface substantially as aparallel beam, while the beam irradiator further comprises moving meansfor scanning the sample in a direction intersecting with the linear orstrip-shaped common region.

The beams are reflected by the first reflector to be substantiallyone-dimensionally diverged and thereafter converted to substantiallyparallel beams by the second reflector, whereby it is possible toirradiate a linear or strip-shaped region which is wider than the beamssupplied from the beam sources with parallel beams from prescribeddirections of incidence. Further, the sample is scanned in a directionintersecting with the linear or strip-shaped region, whereby the beamscan be uniformly applied to a wide target surface. In addition, aplurality of beam sources and a plurality of reflecting means are soprovided that a wide target surface can be uniformly irradiated withbeams from a plurality of directions of incidence.

Each reflecting means preferably further comprises rectifying meanswhich is provided in a path of each beam between the first reflector andthe substrate for regulating the direction of the beam.

The rectifying means is arranged in the beam path between the firstreflector and the substrate, whereby the beams can be regulated in aprescribed direction. Therefore, no strict accuracy is required for theshapes and arrangement of the respective reflectors, whereby theapparatus can be easily structured.

According to the present invention, a beam reflecting device forreflecting a gas beam which is supplied from a beam source therebyenabling irradiation of a target surface of a sample with the gas in aprescribed direction of incidence comprises a first reflector forreflecting the beam thereby generating a divergent beam having a beamsection which is two-dimensionally enlarged with progress of the beam,and a second reflector having a concave reflecting surface for furtherreflecting the divergent beam to be incident upon a linear orstrip-shaped region of the target surface substantially as a parallelbeam.

The beams are reflected by the first reflector to be substantiallyone-dimensionally diverged and thereafter converted to substantiallyparallel beams by the second reflector, whereby it is possible toirradiate a linear or strip-shaped region which is wider than the beamssupplied from the beam sources with the beams.

Accordingly, an object of the present invention is to provide atechnique which can form an axially oriented polycrystalline thin filmoriented in a desired direction and a single-crystalline thin filmhaving a desired crystal orientation on an arbitrary substrate includinga single-crystalline substrate.

Another object of the present invention is to provide a beam irradiatorand a beam reflecting device for enabling efficient formation of asingle-crystalline thin film.

Throughout the specification, the term "substrate" is not restricted toa substance simply serving as a base to be provided thereon with a thinfilm, but generally indicates a medium to be provided thereon with athin film, including a device having a prescribed function, for example.

Throughout the specification, the term "gas beam" is a concept includingall of a beam-type ion current, an atom current and a molecular flow.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a model diagram showing an apparatus which is suitable forcarrying out a method according to a first preferred embodiment of thepresent invention;

FIGS. 2A to 2C are perspective views showing a structure of acollimator;

FIGS. 3A and 3B are sectional views showing a sample;

FIG. 4 is a front sectional view showing an apparatus which is suitablefor carrying out a method according to a second preferred embodiment ofthe present invention;

FIG. 5 is a perspective view showing a reflector which is employed inthe method according to the second preferred embodiment of the presentinvention;

FIGS. 6A, 6B and 6C are a plan view, a side elevational view and a frontelevational view showing an example of the reflector which is employedin the method according to the second preferred embodiment of thepresent invention;

FIG. 7 is a graph showing characteristics of an ECR ion generator whichis employed in the method according to the second preferred embodimentof the present invention;

FIG. 8 illustrates experimental data verifying the method according tothe second preferred embodiment of the present invention;

FIG. 9 is a perspective view showing another example of the reflectoremployed in the method according to the second preferred embodiment ofthe present invention;

FIGS. 10A, 10B and 10C illustrate three surfaces of still anotherexample of the reflector employed in the method according to the secondpreferred embodiment of the present invention;

FIGS. 11A and 11B are structural diagrams showing a further example ofthe reflector employed in the method according to the second preferredembodiment of the present invention;

FIGS. 12A and 12B are structural diagrams showing a further example ofthe reflector employed in the method according to the second preferredembodiment of the present invention; and

FIG. 13 is a front sectional view showing an apparatus which is suitablefor carrying out a method according to a preferred embodiment of thepresent invention.

FIG. 14 is a front sectional view showing an apparatus according to afourth preferred embodiment of the present invention;

FIG. 15 illustrates a result of a verification test in the apparatusaccording to the fourth preferred embodiment of the present invention;

FIG. 16 is a front sectional view showing an apparatus according to afifth preferred embodiment of the present invention;

FIG. 17 is a perspective view showing a reflector in the fifth preferredembodiment;

FIG. 18 is a plan view of the reflector shown in FIG. 17;

FIG. 19 is an exploded perspective view of the reflector shown in FIG.17;

FIG. 20 is an exploded perspective view of the reflector shown in FIG.17;

FIG. 21 is a plan view of the reflector shown in FIG. 17;

FIG. 22 is a sectional view taken along the line A--A in FIG. 21;

FIG. 23 is a perspective view showing an apparatus according to a sixthpreferred embodiment of the present invention;

FIG. 24 is a perspective view showing an apparatus according to aseventh preferred embodiment of the present invention;

FIG. 25 is a process diagram for illustrating a method according to aneighth preferred embodiment of the present invention;

FIG. 26 is a process diagram for illustrating the method according tothe eighth preferred embodiment of the present invention;

FIG. 27 is a process diagram for illustrating the method according tothe eighth preferred embodiment of the present invention;

FIG. 28 is a front sectional view of an apparatus according to a ninthpreferred embodiment of the present invention;

FIG. 29 is a front sectional view showing a reflecting unit in the ninthpreferred embodiment of the present invention;

FIG. 30 is a plan view showing a reflecting unit in the ninth preferredembodiment;

FIG. 31 is a front sectional view showing an apparatus according to atenth preferred embodiment of the present invention;

FIG. 32 is a perspective view showing an apparatus according to aneleventh preferred embodiment of the present invention;

FIG. 33 is a plan view showing the apparatus according to the eleventhpreferred embodiment of the present invention;

FIG. 34 is a front elevational view of the apparatus according to theeleventh preferred embodiment of the present invention;

FIG. 35 is a plan view of the apparatus according to the eleventhpreferred embodiment of the present invention; and

FIG. 36 is a perspective view showing an apparatus according to atwelfth preferred embodiment of the present invention.

FIG. 37 is a process diagram showing a method according to a thirteenthpreferred embodiment of the present invention;

FIG. 38 is a process diagram showing the method according to thethirteenth preferred embodiment of the present invention;

FIG. 39 is a process diagram showing the method according to thethirteenth preferred embodiment of the present invention;

FIG. 40 is a process diagram showing the method according to thethirteenth preferred embodiment of the present invention;

FIG. 41 is a process diagram showing the method according to thethirteenth preferred embodiment of the present invention;

FIG. 42 is a process diagram showing the method according to thethirteenth preferred embodiment of the present invention;

FIG. 43 is a process diagram showing a method according to a fourteenthpreferred embodiment of the present invention;

FIG. 44 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 45 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 46 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 47 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 48 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 49 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 50 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 51 is a process diagram showing the method according to thefourteenth preferred embodiment of the present invention;

FIG. 52 is a process diagram showing a method according to a seventeenthpreferred embodiment of the present invention;

FIG. 53 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 54 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 55 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 56 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 57 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 58 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 59 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 60 is a process diagram showing the method according to theseventeenth preferred embodiment of the present invention;

FIG. 61 is a process diagram showing a method according to an eighteenthpreferred embodiment of the present invention;

FIG. 62 is a front elevational view showing an apparatus according to anineteenth preferred embodiment of the present invention;

FIG. 63 is a plan view showing the apparatus according to the nineteenthpreferred embodiment of the present invention;

FIG. 64 is a front sectional view showing the apparatus according to thenineteenth preferred embodiment of the present invention;

FIG. 65 is a perspective view showing the apparatus according to thenineteenth preferred embodiment of the present invention;

FIG. 66 is a front elevational view showing an apparatus according to atwentieth preferred embodiment of the present invention;

FIG. 67 is a plan view showing an apparatus according to a twenty-firstpreferred embodiment of the present invention;

FIG. 68 is a plan view showing an apparatus according to a twenty-thirdpreferred embodiment of the present invention;

FIG. 69 is a front sectional view showing an apparatus according to atwenty-fourth preferred embodiment of the present invention;

FIG. 70 is a front sectional view showing another apparatus according tothe twenty-fourth preferred embodiment of the present invention;

FIG. 71 is a partially fragmented sectional view showing an apparatusaccording to a twenty-fifth preferred embodiment of the presentinvention;

FIG. 72 is a plan view showing another apparatus according to thetwenty-fifth preferred embodiment of the present invention;

FIG. 73 is a front sectional view showing an apparatus according to atwenty-sixth preferred embodiment of the present invention;

FIG. 74 is a front sectional view showing an apparatus according to atwenty-seventh preferred embodiment of the present invention;

FIG. 75 is a front sectional view showing an apparatus according to atwenty-eighth preferred embodiment of the present invention; and

FIG. 76 is a front sectional view showing an apparatus according to atwenty-ninth preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<A. Formation of Single-Crystalline Thin Film or Axially OrientedPolycrystalline Thin Film>

Preferred embodiments for efficiently forming a single-crystalline thinfilm or axially oriented polycrystalline thin film on a substrate arenow described.

<A-1. First Preferred Embodiment>

A first preferred embodiment of the present invention is now described.

<A-1-1. Structure of Apparatus>

FIG. 1 is a model diagram showing the structure of an apparatus 80 foreffectively implementing a method according to the first preferredembodiment of the present invention. This apparatus 80 is adapted toconvert a polycrystalline thin film 82, which is formed on a substrate81, to a single-crystalline thin film. Therefore, the apparatus 80 issupplied with a sample prepared by the polycrystalline thin film 82 of aprescribed material which is already formed on the substrate 81 by awell-known method.

For example, the substrate 81 is prepared from polycrystalline SiO₂(quartz), and a polycrystalline Si (silicon) thin film 82 is formed onthis quartz substrate 81, to be converted to a single-crystalline Sithin film. The apparatus 80 comprises cage-type ion sources 83. Inertgases are introduced into the ion sources 83 from conduits 84 andionized therein by electron beams, thereby forming plasmas of the inertgases. Further, only ions are extracted from the ion sources 83 byaction of electric fields which are formed by lead electrodes providedin the ion sources 83, whereby the ion sources 83 emit ion beams. Forexample, it is possible to accelerate Ne (neon) ions to 200 to 600 eV bythe ion sources 83 of 10 cm in diameter, for example, with currentdensities of 1 to 9 mA/cm².

The ion beams which are emitted from the ion sources 83 are guided toreflection deaccelerators 85 and collimators 86, and thereafter appliedto the surface of the polycrystalline thin film 82 at prescribed angles.Each reflection deaccelerator 85 is provided with two siliconsingle-crystalline plates having major surfaces of (100) planes. Thesesilicon single-crystalline plates are in the form of discs havingdiameters of 15 cm, for example. These silicon single-crystalline platessuccessively reflect the ion beams which are incident on the majorsurfaces thereof at angles of incidence of 45° to reduce energy levelsand neutralize electric charges thereof, thereby converting the ionbeams to low-energy neutral atomic beams.

FIGS. 2A to 2C are perspective views showing the structure of eachcollimator 86. FIG. 2A is an overall perspective view, FIG. 2B is anenlarged perspective view and FIG. 2C is a further enlarged perspectiveview. The collimator 86 regulates directions of the atomic beams,thereby supplying the polycrystalline thin film 82 with atomic beamshaving high directivity. The collimator 86 is formed by alternatelystacking corrugated members, which are prepared by evaporating siliconfilms 86b on both sides of aluminum plates 86a as shown in FIG. 2C., andflat plate members having similar structures as shown in FIG. 2B. Thiscollimator 86 has 30 layers, for example. Both surfaces of the aluminumplates 86a are covered with the silicon films 86b, so that aluminumatoms which are different atoms will not reach the polycrystalline Sithin film 82 even if the corrugated members and the flat plate membersare struck by an neutral atom current to cause sputtering. The atomicbeams are regularized in direction within a range of ±0.5° while passingthrough thin channels defined between the corrugated and flat platemembers, to be converted to atomic beams having high directivity.

The quartz substrate 81 is mounted on a heater 87, which is adapted tomaintain the quartz substrate 81 at a prescribed high temperature.

<A-1-2. Operation of Apparatus>

The operation of the apparatus 80 is now described. The sample which issupplied to the apparatus 80 can be prepared by forming thepolycrystalline Si thin film 82 on the quartz substrate 81 by well-knownchemical vapor deposition (CVD), for example. The quartz substrate 81 is1.5 mm in thickness, for example, and the polycrystalline Si thin film82 is about 2000Å in thickness, for example. First, the sample asprepared is mounted on the heater 87. This heater 87 maintains thesample, i.e., the quartz substrate 81 and the polycrystalline Si thinfilm 82, at a temperature of 550° C. This temperature is lower than thecrystallization temperature of silicon, whereby no single-crystalline Siis converted to polycrystalline Si under this temperature. However, thistemperature is so high that polycrystalline Si can be grown tosingle-crystalline Si if a seed crystal is present.

Then, Ne (neon) gases are introduced into the ion sources 83 from theconduits 84, to form Ne ion beams. The as-formed Ne ion beams passthrough the reflection deaccelerators 85 and the collimators 86, toreach the surface of the polycrystalline Si thin film 82 as low energyneutral Ne atomic beams. The two Ne atomic beams which are started fromthe two ion sources 83 are incident upon the surface of thepolycrystalline Si thin film 82 at angles of incidence of 35° so thatthe directions of incidence are two-fold symmetrical with each otherabout a normal line on the surface of the polycrystalline Si thin film82. The directions of incidence of these two beams, which are at anangle of 70° to each other, correspond to normal line directions ofindependent two densest planes, i.e., (111) planes of single-crystallineSi having a diamond crystal structure.

The energy levels of the plasmas formed by the ion sources 83 are so setthat the Ne atoms reaching the polycrystalline Si thin film 82 are atlevels causing no sputtering of the polycrystalline Si thin film 82,i.e., at levels lower than a value (=27 eV) known as a threshold energylevel in sputtering of Si caused by irradiation with Ne atoms.Therefore, the so-called law of Bravais acts on the polycrystalline Sithin film 82. Namely, Si atoms provided in the vicinity of the surfaceof the polycrystalline Si thin film 82 are so rearranged that planesperpendicular to the directions of incidence of the Ne atomic beamswhich are applied to the polycrystalline Si thin film 82 define densestcrystal planes.

Since the Ne atomic beams are incident from two directions correspondingto those perpendicular to the independent densest planes of thesingle-crystalline Si, whereby the Si atoms are so rearranged thatplanes perpendicular to the directions of incidence define the densestplanes. Namely, two independent (111) planes are controlled by the twoNe atoms beams having independent directions of incidence to berearranged in constant directions, whereby the crystal orientation isunequivocally decided. Thus, a layer which is close to the surface ofthe polycrystalline Si thin film 82 is converted to a single-crystallineSi layer having a regulated crystal orientation.

The above description corresponds to a first stage ofsingle-crystallization of the polycrystalline Si thin film 82. FIGS. 3Aand 3B are model diagrams showing internal structures of the sample inthe first stage and a following second stage of single-crystallization.In the first stage, a single-crystalline Si layer 88 is formed only inthe vicinity of the surface of the polycrystalline Si thin film 82, asshown in FIG. 3A.

As hereinabove described, the temperature of the polycrystalline Si thinfilm 82 is adjusted to a level which is suitable for growing a seedcrystal. Therefore, the single-crystalline Si layer 88 which is formedon the surface of the polycrystalline Si thin film 82 serves as a seedcrystal, to be grown toward a deep portion of the polycrystalline Sithin film 82. Finally the overall region of the polycrystalline Si thinfilm 82 is converted to the single-crystalline Si layer 88, as shown inFIG. 3B. Thus, a single-crystalline Si thin film having a regulatedcrystal orientation is formed on the quartz substrate 81. Since thepolycrystalline Si thin film 82 is maintained at a temperature which islower than the crystallization temperature of Si as hereinabovedescribed, the single-crystalline Si layer 88 will not return to thepolycrystalline structure, which is a thermal equilibrium state.

The single-crystalline Si layer 88, which is formed on thepolycrystalline Si thin film 82 by irradiation to serve as a seedcrystal, is integrated with a polycrystalline Si layer remaining in itsdeep portion since this layer 88 is converted from the polycrystallineSi thin film 82. Namely, the polycrystalline Si layer 82 is completelyin contact with the seed crystal. Therefore, vertical solid phaseepitaxial growth progresses in an excellent state. Further, the seedcrystal and the single-crystalline Si which is formed by the solid phaseepitaxial growth are single crystals of the same material having thesame crystal orientation, whereby it is not necessary to remove the seedcrystal after formation of the single-crystalline Si thin film 88.Further, the single-crystalline Si thin film 88 is formed by thevertical solid phase epitaxial growth, whereby it is possible toefficiently obtain a desired single-crystalline Si thin film in a shorttime as compared with the prior art utilizing transverse growth.

An element forming the atomic beams which are applied to thepolycrystalline Si thin film 82 is preferably prepared from Ne, ashereinabove described. Since Ne atoms are lighter than Si atoms, thereis a high possibility that the relatively heavy Si atoms rearwardlyscatter the relatively light Ne atoms when the atomic beams are appliedto the Si thin film, whereby the Ne atoms hardly penetrate into the Sithin film to remain therein. Further, the inert element such as Ne isselected as an element forming the as-applied atomic beams since theinert element forms no compound with any element forming the thin filmsuch as Si even if the same remains in the Si thin film, whereby theelectronic/physical properties of the Si thin film are hardly influencedby this element and this element can be easily removed by increasing thetemperature of the as-finished single-crystalline Si thin film to someextent.

The sample is irradiated with the neutralized atomic beams in place ofdirect Ne ion beams, for the following reasons: First, charged particlebeams such as ion beams are spread to lose directivity by repulsionbetween the particles caused by static electricity. Second, charges arestored in the thin film when charged particle beams are employed for thethin film which is made of a material having high resistivity or thelike, such that the beams cannot reach the thin film beyond a certainamount due to repulsion of the stored charges. When neutral atomic beamsare employed, on the other hand, no charges are stored in the thin filmwhile parallel beams having excellent directivity reach the thin film tofacilitate smooth crystallization.

<A-1-3. Other Exemplary Sample>

While the above description has been made on the case of converting thepolycrystalline Si thin film 82 to a single-crystalline Si thin film,the inventive method is applicable not only to a polycrystalline thinfilm but to an amorphous thin film, to attain a similar effect.Experimental data verifying this point is now described.

In the experiment, a sample was prepared by previously forming anamorphous Si thin film on a quartz substrate by plasma CVD. Inert gasesto be applied to the sample were prepared from Ne gases. The quartzsubstrate was 1.5 mm in thickness, and the amorphous Si thin film wasabout 2000 Å in thickness. This sample was mounted on the heater 87, andmaintained at a temperature of 550° C. In this state, the sample wasirradiated with beams for about 20 seconds under conditions ofacceleration voltages of ion sources of 2000 V and current densities of2 mA/cm². As the result, a brown color specific to amorphous Sidisappeared from the as-irradiated central portion of the sample, andthis portion was changed to a slightly yellowish transparent state. Inthis portion, a part of about 1 cm² was examined with X rays and bydirective etching, whereby it was provided that single-crystalline Siwas formed with (110) axes along a normal line direction of thesubstrate.

The crystal orientation was decided by covering the crystal planes withSiO₂ (silicon dioxide) films, forming small holes in these oxide films,etching the same with KOH (potassium hydroxide) and confirming etchingbits. As the result, it was possible to confirm that the etching bitswere hexagonal, thereby confirming that single-crystalline Si having(110) axes in the normal line direction was completed.

<A-2. Second Preferred Embodiment>

A second preferred embodiment of the present invention is now described.

<A-2-1. Overall Structure of Apparatus>

FIG. 4 is a front sectional view showing an apparatus 101 foreffectively implementing a method according to the second preferredembodiment of the present invention. This apparatus 101 is also adaptedto convert a polycrystalline thin film, which is previously formed on asubstrate 11, to a single-crystalline thin film, similarly to theaforementioned apparatus 80.

This apparatus 101 comprises a reaction vessel 1, and an electroncyclotron resonance (ECR) ion generator 2 which is built in an upperportion of the reaction vessel 1. The ECR ion generator 2 comprises aplasma container 3 which defines a plasma chamber 4 in its interior. Amagnetic coil 5 is provided around the plasma container 3, to apply a dchigh magnetic field to the plasma chamber 4. Further, a waveguide 6 andan inlet pipe 7 are provided on an upper surface of the plasma container3 for introducing a microwave and an inert gas such as Ne gas into theplasma chamber 4 respectively.

The reaction vessel 1 defines an reaction chamber 8 in its interior. Thebottom portion of the plasma container 3 defines an outlet 9 for passinga plasma in its center. The reaction chamber 8 and the plasma chamber 4communicate with each other through the outlet 9. In the interior of thereaction chamber 8, a sample holder 10 is arranged on a positionimmediately under the outlet 9. The substrate 11 is placed on the sampleholder 10, while a reflector 12 is placed to be located above thesubstrate 11. The sample holder 10 comprises a heater (not shown), toheat the substrate 11 and hold the same at a proper high temperaturelevel.

The reflector 12 is preferably made of a metal. The sample holder 10 iscoupled to a rotation driving mechanism (not shown), to be rotatable ina horizontal plane. Further, the sample holder 10 can horizontally movethe substrate 11 while fixing the reflector 12.

The reaction chamber 8 communicates with an evacuation pipe 14. An endof the evacuation pipe 14 is coupled with a vacuum unit (not shown) toevacuate the reaction chamber 8 through the evacuation pipe 14, therebymaintaining the reaction chamber 8 at a prescribed degree of vacuum. Avacuum gauge 15 for displaying the degree of vacuum in the reactionchamber 8 is provided in communication with the reaction chamber 8.

<A-2-2. Structure of Reflector>

FIG. 5 is a perspective view showing an exemplary reflector 12a. Thisreflector 12a is adapted to form a single crystal having a diamondstructure, such as single-crystalline Si. The reflector 12a defines anopening on a central portion of a flat plate type base 21. Three blocks22 in the form of rectangular parallelopipeds are fixedly providedaround the opening, and reflecting blocks 23 are fixed to inner sides ofthe blocks 22 respectively. Consequently, an equilateral triangularopening 24 which is trimmed with the reflecting blocks 23 is defined atthe central portion of the base 21. In the reflecting blocks 23, slopes25 facing the opening 24 serve as reflecting surfaces for reflecting agas beam. Therefore, the angles of inclination of the slopes 25 are setat proper levels in correspondence to the directions of crystal axes ofthe single crystal to be formed.

FIGS. 6A, 6B and 6C are a plan view, a side elevational view and a frontelevational view of the reflector 12a which is formed by the blocks 22and the reflecting blocks 23 respectively. As shown in FIG. 6B, theangle of inclination of each slope 25 is set at 55°. The reflector 12ais in a structure not fixing the substrate 11, whereby the substrate 11can be relatively horizontally moved with respect to the reflector 12a.Therefore, it is possible to form a single-crystalline thin film on thesubstrate 11 having a large area by horizontally moving the substrate 11while fixing the reflector 12a on the sample holder 10.

<A-2-3. Operation of ECR Ion Generator>

Referring again to FIG. 4, the operation of the ECR ion generator 2 isnow described. An inert gas such as Ne gas or Ar gas is introduced fromthe inert gas inlet pipe 7 into the plasma chamber 4, while a microwaveis simultaneously introduced from the waveguide 6 into the plasmachamber 4. Further, a dc current is also simultaneously supplied to themagnetic coil 5, to form a dc magnetic field in the plasma chamber 4 andits periphery. The gas as supplied is maintained in a plasma state byactions of the microwave and the dc magnetic field. This plasma isformed by high-energy electrons which are in screw motion in theprinciple of cyclotron by the microwave and the dc magnetic field.

These electrons, which have diamagnetic properties, are moved to aweaker magnetic field side, to form an electron stream along a line ofmagnetic force. Consequently, positive ions also form an ion currentalong the line of magnetic force following the electron stream, in orderto maintain electrical neutrality. In other words, the electron streamand the ion current are downwardly directed from the outlet 9 into thereaction chamber 8. The ion current and the electron stream thus flowingin parallel with each other are recombined with each other after a lapseof a deionization time, to form a neutral atom current. Therefore,substantially only a neutral atom current is formed in a positiondownwardly separated from the outlet 9 beyond a prescribed distance.

FIG. 7 is a graph showing the result of relation between ion currentdensity and the distance from the outlet 9 actually measured when Ar⁺ions of 10 eV were discharged from the outlet 9 by the ECR ion generator2. It is understood from this graph that the ion current density isabruptly reduced at a distance of about 4 to 5 cm from the outlet 9, andattenuated to a level of 1/10 to 1/12 at a position of 14 cm. Theneutral atom current is increased by such attenuation of the ioncurrent, whereby substantially only a neutral atom current downwardlyflows in a position downwardly separated from the outlet 9 by at least14 cm.

Thus, the ECR ion generator 2 for generating ions forms an ion currentin parallel with the electron stream, whereby it is possible to easilyobtain a neutral atom current having high density by employing the ECRion generator 2, with no employment of other means for neutralizing theion current. Since the ion current is formed in parallel with theelectron stream, further, it is possible to obtain an ion current whichis close to a parallel current having a regulated direction of progresssubstantially with no divergence. Since the parallel ion current isconverted to the neutral atom current, the atom current is also close toa parallel current having a regulated direction of progress.

<A-2-4. Operation of Apparatus 101>

Referring again to FIG. 4, the operation of the apparatus 101 is nowdescribed. It is assumed that the reflector 12 is implemented by thereflector 12a shown in FIGS. 5 and 6A to 6C and the substrate 11 isprepared from polycrystalline SiO₂ (quartz), so that asingle-crystalline Si thin film is formed on the quartz substrate 11. Apolycrystalline Si thin film is previously formed on the quartzsubstrate 11 by a well-known method such as CVD.

First, the sample is mounted between the sample holder 10 and thereflector 12a (12). The heater provided in the sample holder 10 holdsthe sample, i.e., the quartz substrate 11 and the polycrystalline Sithin film, at a temperature similar to that in the first preferredembodiment, i.e., a temperature of 550° C.

An inert gas which is introduced from the inert gas inlet pipe 7 ispreferably prepared from Ne gas having a smaller atomic weight than Siatoms. Due to the action of the ECR ion generator 2, an Ne⁺ ion currentand an electron stream are formed downwardly from the outlet 9. Thedistance between the outlet 9 and the reflector 12a (12) is preferablyset at a sufficient level for substantially converting the Ne⁺ ioncurrent to a neutral Ne atom current. The reflector 12a (12) is set in aposition receiving the downwardly directed Ne atom current.

A part of the downwardly directed Ne atom current is reflected by thethree slopes 25 which are formed in the reflector 12a, to be applied tothe polycrystalline Si thin film provided on the SiO₂ substrate 11through the opening 24. Another part of the Ne atom current is notincident upon the slopes 25 but directly incident upon thepolycrystalline Si thin film through the opening 24. In other words, thepolycrystalline Si thin film is irradiated with four Ne atom currentcomponents, i.e., a component straightly received from the outlet 9 andthree components reflected by the three slopes 25. Since the angles ofinclination of the slopes 25 are set at 55°, directions of incidence ofthe four Ne atom current components correspond to four directions whichare perpendicular to four independent densest crystal planes of the Sisingle crystal to be formed, i.e., (111) planes.

The energy of the plasma which is formed by the ECR ion generator 2 isso set that the Ne atoms reaching the SiO₂ substrate 11 are at energylevels which are lower than threshold energy (=27 eV) in sputtering ofSi by irradiation with Ne atoms. Therefore, the law of Bravais acts onthe polycrystalline Si thin film. As the result, the Si atoms in thepolycrystalline Si thin film are so rearranged that planes which areperpendicular to the direction of incidence of the Ne atomic current asapplied define densest crystal planes. Since the Ne atom current asapplied has four components which are incident in directionscorresponding to those perpendicular to four independent densest planesof the single-crystalline Si, the Si atoms are so rearranged that allplanes perpendicular to the directions of incidence define the densestplanes. Namely, the directions of rearrangement of the four independent(111) planes are controlled by four Ne atomic beams having directions ofincidence which are independent of each other, whereby the crystalorientation is univocally decided. Thus, a layer in the vicinity of thesurface of the polycrystalline Si thin film is converted to asingle-crystalline Si layer having a regulated crystal orientation.

The temperature of the polycrystalline Si thin film 82 is adjusted to550° C., i.e., a level within a range suitable for growing a seedcrystal. Therefore, the single-crystalline Si layer which is formed onthe surface of the polycrystalline Si thin film 82 serves as a seedcrystal, to be grown toward a deep portion of the polycrystalline Sithin film 82. Then, the overall region of the polycrystalline Si thinfilm 82 is converted to a single-crystalline Si layer. Thus, asingle-crystalline Si layer having a regulated crystal orientation isformed on the quartz substrate 11. The aforementioned FIGS. 3A and 3Btypically express the aforementioned formation of the single-crystallineSi layer and the process of its growth.

As hereinabove described, the reflector 12 is preferably made of ametal, since Ne⁺ ions are converted to neutral atoms when an Ne⁺ ioncurrent which is slightly mixed in the neutral Ne atom current isreflected by the conductive reflector 12, so that the substrate 11 isirradiated with the as-converted neutral Ne atom current. The neutralatom current is advantageously incident upon the substrate 11 as a flowhaving a regulated direction since its direction of progress hardlydiverges dissimilarly to an ion current.

In the process of irradiating the sample with the Ne atomic current, therotation driving mechanism (not shown) may be driven to rotate thesample holder 10. Thus, it is possible to improve homogeneity indistribution of an amount of irradiation on the polycrystalline Si thinfilm.

<A-2-5. Valid Data>

Description is now made on a test verifying formation of asingle-crystalline thin film by the method according to the secondpreferred embodiment. FIG. 8 illustrate experimental data showingelectron beam diffraction images of samples comprising polycrystallineSiO₂ substrates and single-crystalline Si thin films formed thereon onthe basis of the aforementioned method. The sample was obtained byirradiating a substrate with four Ne atom current components using areflector.

In this sample, three-fold rotation-symmetrical diffraction spots wereobtained as shown in FIG. 8. This verifies that the as-obtained samplewas formed as single-crystalline Si having regulated crystal axes. Sinceit was possible to convert a polycrystalline Si thin film having apolycrystalline structure of higher regularity in atomic arrangementthan an amorphous structure to a single-crystalline Si thin film, it isconceivably decided possible to convert a thin film having an amorphousstructure such as amorphous Si to a single-crystalline thin film, as amatter of course.

<A-2-6. Methods of Forming Single-Crystalline Thin Films other than SiThin Film>

While the structure and the operation of the apparatus 101 have beendescribed with reference to formation of a single-crystalline Si thinfilm, it is also possible to form single-crystalline thin films otherthan an Si thin film through the apparatus 101.

                  TABLE 1                                                         ______________________________________                                        Gas Material for Crystal Forming Step                                         ______________________________________                                        for GaAs                                                                      Ion Beam        Ar, Ne                                                        Element         Ga(CH.sub.3).sub.3                                                            AsH.sub.3                                                     Impurity        Zn(CH.sub.3).sub.3, Zn(C.sub.2 H.sub.5).sub.3 (p-type)                        SiH.sub.4 (n-type)                                            for GaN                                                                       Ion Beam        Ar, Ne, NH.sub.3                                              Element         Ga(CH.sub.3).sub.3                                                            NH.sub.3                                                      Impurity        Zn(CH.sub.3).sub.3, Zn(C.sub.2 H.sub.5).sub.3 (p-type)                        SiH.sub.4 (n-type)                                            for Si                                                                        Ion Beam        Ne                                                            Element         SiH.sub.4                                                                     Si.sub.2 H.sub.6                                              Impurity        B.sub.2 H.sub.3 (p-type)                                                      AsH.sub.3 (n-type)                                                            PH.sub.3 (n-type)                                             ______________________________________                                    

Table 1 shows values of sputtering threshold energy in variouscombinations of types of atoms or ions as applied and elements formingtarget thin films. In each combination, it is necessary to apply an ioncurrent or an atom current which is at a lower energy level than theas-listed threshold energy. As to thin films formed by compounds, referto threshold energy levels related to elements having the maximum atomicweights among the elements. The values shown in Table 1 have beenobtained on the basis of simulation, unless otherwise stated.

When the thin film as irradiated is formed not by a simple substancesuch as Si but a compound such as GaAs, for example, it is advisable toapply atoms which are lighter than an element having the maximum atomicweight. Further, beams of a compound such as those of N₂ may be appliedin place of beams of simple atoms, for example. In this case, an element(for example, N atoms) forming the compound is preferably lighter thanthe element having the maximum atomic weight forming the thin film asirradiated.

<A-2-7. Other Examples of Reflector>

Description is now made on other exemplary structures of the reflector.FIGS. 9 and 10A to 10C illustrate a reflector 12b for forming asingle-crystalline thin film having a diamond crystal structure whose(111) planes define densest planes, similarly to the reflector 12a shownin FIG. 5. FIG. 9 is a perspective view of the reflector 12b, and FIGS.10A to 10C illustrate three surfaces thereof. This reflector 12b isprovided with a groove 31a for sliding the substrate 11 on an uppersurface of a base 31 which is mounted on the sample holder 10, so thatthe substrate 11 is built in the base 31. Therefore, the substrate 11 isfixed to the groove 31a when the same is irradiated, dissimilarly to thereflector 12a. Bottom surfaces of reflecting blocks 33 are placed on theupper surface of the base 31, so that the reflecting blocks 33 arelocated on the substrate 11. As shown in FIG. 10B, the angles ofinclination of slopes 35 provided in the reflecting blocks 33 are set at55°, similarly to those of the reflector 12a.

It is also possible to form a single-crystalline thin film having acrystal structure other than a diamond structure. In this case, stillanother reflector may be prepared to have a crystal structure which issuitable for the target crystal structure. Further, it is also possibleto form a single-crystalline thin film having various crystalorientations in the same crystal structure. In this case, a reflectorwhich is suitable for respective crystal orientations is prepared, ashereinafter described.

FIGS. 11A and 11B illustrate an exemplary reflector 12c corresponding toa single crystal of a diamond structure, whose (100) planes are parallelto a substrate surface. FIG. 11A is a front sectional view taken alongthe line A--A in FIG. 11B, which is a plan view showing the reflector12c. A groove 42 is formed on an upper surface of a flat plate type base41. The substrate 11 is inserted in this groove 42. Namely, thereflector 12c is adapted to receive the substrate 11, which cannot berelatively horizontally moved with respect to the reflector 12c when thesame is irradiated. This ba se 41 is p laced on the sample holder 10.

Four reflecting blocks 43 are arranged on the base 41 around thesubstrate 11, to be perpendicularly adjacent to each other. A shieldingplate 46 having openings 47 only above slopes 45 of the reflectingblocks 43 is set on upper surfaces of the reflecting blocks 43. An atomcurrent or an ion current which is incident upon the shielding plate 46downwardly from above passes through the openings 47 alone, to beentirely reflected by the slopes 45. Namely, only four components of theatom current or the ion current as reflected are incident upon thesubstrate 11, with no presence of a component which is directly incidentfrom the above. The angles of inclination of the slopes 45 are set at62.63°. Therefore, the directions of incidence of the four componentsmatch with directions perpendicular to four (111) planes, which areindependent of each other, in the crystal of the diamond structure.

FIGS. 12A and 12B illustrate a reflector 12d corresponding to a singlecrystal of a diamond structure whose (110) planes are parallel to asubstrate surface. FIG. 12A is a front sectional view taken along theline B--B in FIG. 12B, which is a plan view showing the reflector 12d. Agroove 52 is formed on an upper surface of a base 51 having an angle ofinclination of 35°. The substrate 11 is inserted in this groove 52.Namely, this reflector 12d is adapted to receive the substrate 11, whichcannot be relatively horizontally moved with respect to the reflector12d when the same is irradiated. This base 51 is placed on the sampleholder 10.

A single reflecting block 53 is arranged on the base 51. A slope 55 ofthe reflecting block 53 is set at an angle of inclination of 90° withrespect to the upper surface of the base 51. Therefore, an atom currentor an ion current which is incident from above is divided into twocomponents including that which is directly incident upon the substrate11 at an angle of incidence of 35° and that which is reflected by theslope 55 and incident from an opposite side similarly at an angle ofincidence of 35°. Directions of incidence of these components match withdirections which are perpendicular to two independent planes among fourindependent (111) planes in the crystal of a diamond structure. Namely,these two components define directions of two densest planes which areindependent of each other, whereby it is possible to form asingle-crystalline thin film of a diamond structure having a regulatedcrystal orientation so that the (110) planes are parallel to thesubstrate surface by employing the reflector 12d.

<A-3. Third Preferred Embodiment>

A third preferred embodiment of the present invention is now described.

<A-3-1. Overall Structure of Apparatus>

FIG. 13 is a front sectional view showing a structure of asingle-crystalline thin film forming apparatus 100 for effectivelyimplementing a method of forming a single-crystalline thin filmaccording to a preferred embodiment of the present invention. In FIG.13, the identical numerals are employed with FIG. 4 to represent theidentical components, and therefore, the detailed description of thenumerals in FIG. 13 is omitted. Similarly to the apparatus 101, theapparatus 100 comprises a reaction vessel 1, and an electron cyclotronresonance (ECR) ion generator 2 which is built in an upper portion ofthe reaction vessel 1. In the interior of the reaction chamber 8, asample holder 10 is arranged on a position immediately under the outlet9. In this apparatus 101, the sample holder 10 is not required tocomprise a heater. A substrate 11 is placed on the sample holder 10,while a reflector 12 is placed to be located above the substrate 11. Thesubstrate 11, which is a flat plate of a material having apolycrystalline structure or an amorphous structure, is one of elementsforming a sample. A desired single-crystalline thin film is formed onthis substrate 11. The reflector 12a (FIG. 5, FIGS. 6A to 6C), 12b (FIG.9, FIGS. 10A and 10B), 12c (FIGS. 11A and 11B) or 12b (FIGS. 12A and12B) can be adopted as the reflector 12.

The reaction chamber 8 communicates with reaction gas supply pipes 13.Reaction gases are supplied through the reaction gas supply pipes 13,for forming a thin film of a prescribed material on the substrate 11 byplasma CVD. The preferred embodiment shown in FIG. 1 is provided withthree reaction gas supply pipes 13a, 13b and 13c. Similarly to theapparatus 101, an end of the evacuation pipe 14 is coupled with a vacuumunit (not shown) to evacuate the reaction chamber 8 through theevacuation pipe 14, thereby maintaining the reaction chamber 8 at aprescribed degree of vacuum.

<A-3-2. Operation of Apparatus 100>

The operation of the apparatus 100 is now described. It is assumed thatthe reflector 12 is implemented by the reflector 12a shown in FIGS. 5and 6A to 6C and the substrate 11 is prepared from polycrystalline SiO₂(quartz), so that a thin film of single-crystalline Si is formed on thequartz substrate 11. The reaction gas supply tubes 13a, 13b and 13csupply SiH₄ (silane) gas for supplying Si, which is a main material forthe single-crystalline Si, and B₂ H₃ (diborane) gas and PH₃ (phosphine)gas for doping the substrate 11 with p-type and n-type impuritiesrespectively. An inert gas which is introduced from the inert gas inletpipe 7 is preferably prepared from Ne gas having a smaller atomic weightthan Si atoms.

Due to the action of the ECR ion generator 2, an Ne⁺ ion current and anelectron stream are formed downwardly from the outlet 9. The distancebetween the outlet 9 and the reflector 12a (12) is preferably set at asufficient level for substantially converting the Ne⁺ ion current to aneutral Ne atom current. The reflector 12a (12) is set in a positionreceiving the downwardly directed Ne atom current. The silane gas whichis supplied from the reaction gas supply tube 13a is dashed against theSiO₂ substrate 11 by the Ne⁺ ion current or the Ne atom current.Consequently, a plasma CVD reaction progresses on the upper surface ofthe SiO₂ substrate 11, to grow a thin film formed by Si which issupplied by the silane gas, i.e., an Si thin film. On the other hand,the diborane gas or the phosphine gas is supplied with a properlyadjusted flow rate, whereby a plasma CVD reaction caused by this gasalso progresses to form the Si thin film containing B (boron) or P(phosphorus) in desired density.

The SiO₂ substrate 11 is not heated and hence maintained substantiallyat an ordinary temperature, whereby the Si thin film is grownsubstantially under the ordinary temperature. In other words, the Sithin film is formed at a temperature not more than a level facilitatingcrystallization by plasma CVD. Thus, the Si thin film is first formed asan amorphous Si film by plasma CVD.

A part of the downwardly directed Ne atom current is reflected by thethree slopes 25 which are formed in the reflector 12a, to be incidentupon the upper surface of the SiO₂ substrate 11 through the opening 24.Another part of the Ne atom current is not incident upon the slopes 25but directly incident upon the upper surface of the SiO₂ substrate 11through the opening 24. In other words, the Si thin film being formed onthe upper surface of the SiO₂ substrate 11 is irradiated with four Neatom current components, i.e., a component straightly received from theoutlet 9 and three components reflected by the three slopes 25. Sincethe angles of inclination of the slopes 25 are set at 55°, directions ofincidence of the four Ne atom current components correspond to fourdirections which are perpendicular to four independent densest crystalplanes of the Si single crystal to be formed, i.e., (111) planes.

The energy of the plasma which is formed by the ECR ion generator 2 isso set that the Ne atoms reaching the SiO₂ substrate 11 are at energylevels causing no sputtering in the as-formed Si thin film, i.e., levelslower than the threshold energy level in sputtering of Si by irradiationwith Ne atoms (=27 eV). Therefore, the law of Bravais acts on theas-grown amorphous Si thin film. Namely, the Si atoms in the amorphousSi are rearranged so that planes which are perpendicular to the Ne atomcurrent components applied to the amorphous Si define densest crystalplanes. Since the Ne atom current as applied has four components whichare incident in directions corresponding to those perpendicular to thedensest planes of the single-crystalline Si having a single crystalorientation, the Si atoms are so rearranged that all planesperpendicular to the directions of incidence of the respectivecomponents define the densest planes. The directions of the (111) planesare controlled by the plurality of components of the Ne atom currenthaving directions of incidence which are independent of each other,whereby single-crystalline Si having a single crystal orientation isformed by such rearrangement of the Si atoms. In other words, theamorphous Si thin film being grown by plasma CVD is sequentiallyconverted to a single-crystalline Si thin film having a regulatedcrystal orientation.

The diborane gas or the phosphine gas is supplied by the reaction gassupply pipe 13b or 13c simultaneously with the silane gas, therebyforming a p-type or n-type single-crystalline Si thin film containing Bor P. It is also possible to form an equiaxed n-type single-crystallineSi layer on a p-type single-crystalline Si layer, for example, byalternating these reaction gases containing impurity elements.

As hereinabove described, the SiO₂ substrate 11 is not heated and the Sithin film is formed under a temperature which is lower than thatfacilitating crystallization by plasma CVD. This is because the crystalorientation is arbitrarily directed regardless of the directions of theNe atom current components and cannot be controlled while a polycrystalis inevitably formed under a high temperature facilitatingcrystallization of Si by plasma CVD alone with no application of the Neatom current components.

As described in the first preferred embodiment, Ne which is lighter thanSi atoms is preferably selected as an element forming the atom currentwhich is applied to the Si thin film. As described in the secondpreferred embodiment, the reflector 12 is preferably made of a metal.

In the apparatus 100, conversion to a single crystal sequentiallyprogresses at the same time in the process of growth of the Si thin filmby plasma CVD. Thus, it is possible to form a single-crystalline Si thinfilm having a large thickness under a low temperature. Since asingle-crystalline thin film can be formed under a low temperature, itis possible to further form a new single-crystalline thin film on asubstrate which is already provided with a prescribed device withoutchanging properties of the device, for example.

Thus, it is possible to form a single-crystalline thin film not only ona substrate which serves only as a support member for a thin film but ona substrate of a device having a prescribed structure and functions inthis apparatus 100.

An experimental test was performed in order to verify the formation of asingle-crystalline thin film by the aforementioned method. A similarelectron beam diffraction image to that shown in FIG. 8 was observed fora sample comprising polycrystalline SiO₂ substrates andsingle-crystalline Si thin films formed thereon.

This verifies that the sample obtained by use of the reflector 12 wasformed as single-crystalline Si having regulated crystal axes. Since itwas possible to form a single-crystalline Si thin film on an SiO₂substrate of a polycrystalline structure having higher regularity thanan amorphous structure in atomic arrangement, it is conceivably decidedpossible to form a single-crystalline thin film on a substrate having anamorphous structure, such as an amorphous Si substrate, as a matter ofcourse.

<A-3-3. Preferred Methods of Forming Single-Crystalline Thin Films otherthan Si Thin Film>

While the structure and the operation of the apparatus 100 have beendescribed with reference to formation of a single-crystalline thin film,it is also possible to form single-crystalline thin films other than anSi thin film through the apparatus 100. Tables 2 to 5 show conditionsfor forming semiconductor single-crystalline thin films havingrelatively high demands, including the Si thin film as alreadydescribed, for example. Table 2 shows types of inert gases and reactiongases as supplied.

Tables 3 to 5 show reaction gas flow rates, inert gas flow rates andother process control conditions in formation of respectivesemiconductor single-crystalline thin films.

                  TABLE 2                                                         ______________________________________                                        Threshold Energy                                                              Incident Ion (*Actually Measured Value)                                                                                   Hg                                                                            (Actually                                                                     Measured                          Target He       Ne     Ar    Kr   Xe   Hg   Value)                            ______________________________________                                        Al     127       59     59   77   100  136  120˜140                     Si      60       27     27   35   45   61   60˜70                                               25*                                                   GaAs                    25*                                                   Ge     225       66     49   45   48   57   40˜50                       Ta     1620     385    233   233  159  147  120˜140                     W      1037     245    147   100  89   87   89˜87                       Pt     850      198    118   79   69   67   70˜90                       ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Process Control Condition for Forming Si                                      ______________________________________                                        Gas Flow Rate                                                                 SiH.sub.4 or Si.sub.2 H.sub.6                                                                  5 sccm (1 × 10.sup.-5 ˜4 × 10.sup.-5                        mol/min)                                                     AsH.sub.3        5 sccm (5 × 10.sup.-7 mol/min) for n-type              (Diluted to 10% with Ne)                                                                       Crystal                                                      B.sub.2 H.sub.6  5 sccm (5 × 10.sup.-7 mol/min) for p-type              (Diluted to 10% with Ne)                                                                       Crystal                                                      Ne (for ECR Chamber)                                                                           25 sccm (1 × 10.sup.-3 mol/min)                        Substrate Temperature                                                                          Room Temperature                                             (SiO.sub.2 Substrate)                                                         Degree of Vacuum                                                              Back Pressure    ˜10.sup.-7 Torr                                        Operating Pressure                                                                             1 × 10.sup.-4 ˜4 × 10.sup.-4 Torr          Microwave Power (2.34 GHz)                                                                     300 W                                                        Growth Rate      2 μ/hr                                                    ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Process Control Condition for Forming GaN                                     ______________________________________                                        Gas Flow rate                                                                 TMG (Trimethyl Gallium)                                                                     Bubbler employed. Held at -12° C.˜10°                     C.                                                              Carrier Gas N.sub.2                                                                         5 sccm (1 × 10.sup.-5 ˜4 × 10.sup.-5                        mol/min)                                                        NH.sub.3      10 sccm (4 × 10.sup.-4 mol/min)                           DMZ (Dimethyl Zinc)                                                                         for Forming p-type Crystal                                      Carrier Gas N.sub.2                                                                         5 sccm (1 × 10.sup.-5 ˜2.4 × 10.sup.-5                      mol/min)                                                        SiH.sub.4     for Forming n-type Crystal                                      (Diluted to 10% with Ne)                                                                    5 sccm (1 × 10.sup.-5 ˜2.4 × 10.sup.-5                      mol/min)                                                        Ne (For ECR Chamber)                                                                        15 ccm (7 × 10.sup.-4 mol/min)                            Substrate Temperature                                                                       370° C.                                                  (Si Substrate)                                                                Degree of Vacuum                                                              Back Pressure ˜10.sup.-7 Torr                                           Operating Pressure                                                                          1 × 10.sup.-4 ˜4 × 10.sup.-4 Torr             Microwave Power (2.34                                                                       300 W                                                           GHz)                                                                          Growth Rate   0.1˜0.3 μ/hr                                           ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Process Control Condition for Forming GaAs                                    ______________________________________                                        Gas Flow rate                                                                 TMG (Trimethyl Gallium)                                                                     Bubbler employed. Held at -12° C.˜10°                     C.                                                              Carrier Gas Ar                                                                              5 sccm (1 × 10.sup.-5 ˜4 × 10.sup.-5                        mol/min)                                                        AsH.sub.3     10 sccm (4 × 10.sup.-4 mol/min)                           (Diluted to 10% with Ar)                                                      DMZ (Dimethyl Zinc)                                                                         for Forming p-type Crystal                                      Carrier Gas Ar                                                                              5 sccm (1 × 10.sup.-5 ˜2.4 × 10.sup.-5                      mol/min)                                                        H.sub.2 Te    for Forming n-type Crystal                                      (Diluted to 10% with Ar)                                                                    5 sccm (1 × 10.sup.-5 ˜2.4 × 10.sup.-5                      mol/min)                                                        Ar (For ECR Chamber)                                                                        15 ccm (7 × 10.sup.-4 mol/min)                            Substrate Temperature                                                                       500° C.                                                  (Si Substrate)                                                                Degree of Vacuum                                                              Back Pressure ˜10.sup.-7 Torr                                           Operating Pressure                                                                          1 × 10.sup.-4 ˜4 × 10.sup.-4 Torr             Microwave Power (2.34                                                                       300 W                                                           GHz)                                                                          Growth Rate   0.1˜0.3 μ/hr                                           ______________________________________                                    

Thus, in each of the apparatuses 100 and 101, it is possible to form notonly the aforementioned Si single-crystalline thin film but varioustypes of single-crystalline thin films on substrates such as compoundsingle-crystalline thin films of GaAs, GaN and the like and asingle-crystalline thin film of an insulator such as SiO₂, for example.

<A-4. Modifications of First to Third Preferred Embodiments>

(1) In the first or second preferred embodiment, in order to formsingle-crystalline thin film of GaN, for example, a polycrystalline GaNfilm may be first grown on an Si substrate by general CVD. Thereafter,by use of the apparatus 101, for example, N₂ (nitrogen) gas or NH₃(ammonia) gas containing N atoms may be introduced into the inert gasinlet pipe 7, to irradiate the GaN thin film with a molecular flow ofthe gas or a dissociated N atom current. N atoms which may remain in theinterior of GaN are assembled into the single crystal as an elementforming GaN, and hence there is no possibility of exerting a badinfluence on properties of GaN.

(2) In the first or second preferred embodiment, in order to form a GaAssingle-crystalline thin film, a GaAs polycrystalline thin film may befirst grown on an Si substrate by general molecular beam epitaxy, sothat conditions identical to those for forming an Si single-crystallinethin film are employed except that the substrate temperature ismaintained at 500° C., the gas as applied is prepared from low-priced Argas and the reflector is prepared from a Ta plate. It was possible toobtain a GaAs single-crystalline thin film by this method.

(3) In the third preferred embodiment, in order to formsingle-crystalline thin film of GaN, for example, N₂ (nitrogen) gas orNH₃ (ammonia) gas containing N atoms may be introduced into the inertgas inlet pipe 7 of the apparatus 100, to irradiate the GaN thin filmwith a molecular flow of the gas or a dissociated N atom current.Nitrogen which may remain in the interior of GaN is assembled into thesingle crystal as an element forming GaN, and hence there is nopossibility of exerting a bad influence on properties of GaN.

(4) In place of the reflector 12, ECR ion generators 2 may be providedin a number corresponding to that of components of an atom current whichis applied to the thin film, to directly apply the atom current from theECR ion generators 2 to the thin film. As compared with this method,however, the method shown in FIG. 4 or FIG. 13 employing a single ECRion generator 2 and a single reflector 12 is superior since theapparatus can be simplified in structure and it is possible to maintaina high degree of vacuum in the reaction chamber 8.

In the apparatus 100, further, the ECR ion generator 2 also serves as anenergy source which is required for providing energy to the reaction gasfor carrying out plasma CVD. Namely, the method shown in FIG. 13employing a single ECR ion generator 2 and a single reflector 12 has aspecific advantage such that the same can be carried out by simplyadding the reflector 12 to a structure which is originally necessary forcarrying out plasma CVD.

(5) The ECR ion generator 2 may be replaced by another ion source suchas a Cage type or Kaufmann type one. In this case, however, flow of theas-formed ion current is inclined to be diffused by repulsion caused bystatic electricity between ions, leading to reduction of directivity.Therefore, it is desirable to provide means for neutralizing ions andconverting the same to an atom current or means for improving thedirectivity such as a collimator in a path of the ion current. When anelectrical insulating substrate is employed as the substrate 11, inparticular, it is desirable to provide the means for neutralizing ionsin order to prevent the progress of irradiation from being disabled dueto storage of charges in the substrate 11. Alternatively, the reflector12 may be made of a conductive material such as a metal, tosimultaneously carry out reflection of the ion current and conversion toa neutral atom current.

In the aforementioned method employing the ECR ion generator 2, on theother hand, a neutral atom current can be easily obtained in a formclose to a parallel current with no employment of means for neutralizingthe ion current. Therefore, the thin film can be easily irradiated withan atom current having high incidence angle accuracy. Since a neutralatom current is mainly incident upon the thin film, further, thesubstrate 11 can be prepared from an insulating substrate such as anSiO₂ substrate.

<A-5. Fourth Preferred embodiment>

Next, an apparatus according to a fourth preferred embodiment of thepresent invention is described.

FIG. 14 is a front sectional view showing the overall structure of anaxially oriented polycrystalline thin film forming apparatus 122according to the fourth preferred embodiment. This apparatus 122 isadapted to grow a thin film of a prescribed material on a substrate andto simultaneously convert the thin film to a uniaxially orientedpolycrystalline thin film, thereby forming an axially orientedpolycrystalline thin film on the substrate. This apparatus 122 ischaracteristically different from the apparatus 100 shown in FIG. 13 inthat a reflector 12 is not provided therein.

Referring to FIG. 14, the operation of the apparatus 122 is nowdescribed. It is assumed that the substrate 11 is prepared frompolycrystalline SiO₂ (quartz), so that a thin film of single-crystallineSi is formed on the quartz substrate 11. The reaction gas supply tubes13a, 13b and 13c supply SiH₄ (silane) gas for supplying Si, which is amain material for the single-crystalline Si, and B₂ H₃ (diborane) gasand PH₃ (phosphine) gas for doping the substrate 11 with p-type andn-type impurities respectively. The inert gas introduced from the inertgas inlet pipe 7 is preferably prepared from Ne gas, which has smalleratomic weight than Si atoms and is inert gas.

Due to the action of the ECR ion generator 2, an Ne⁺ ion current and anelectron current are formed downwardly from the outlet 9. The distancebetween the outlet 9 and the substrate 11 is preferably set at a valuewhich is sufficient for converting most part of the Ne⁺ ion current to aneutral Ne atom current. The silane gas which is supplied from thereaction gas supply tube 13a is dashed against the substrate 11 by theNe⁺ ion current or the Ne atom current. Consequently, a plasma CVDreaction progresses on the upper surface of the substrate 11, to grow athin film formed by Si which is supplied by the silane gas, i.e., an Sithin film. On the other hand, the diborand gas or the phosphine gas issupplied with a properly adjusted flow rate, whereby a plasma CVDreaction caused by this gas also progresses to form the Si thin filmcontaining B (boron) or P (phosphorus) in desired density.

The substrate 11 is not heated and hence maintained substantially at anordinary temperature. Therefore, the Si thin film is grown substantiallyunder the ordinary temperature. In other words, the Si thin film isformed at a temperature not more than a level facilitatingcrystallization by plasma CVD. Thus, the Si thin film is first formed asan amorphous Si film by plasma CVD.

The aforementioned downwardly directed Ne atom current isperpendicularly incident upon the upper surface of the substrate 11.Namely, the Si thin film being formed on the upper surface of thesubstrate 11 is irradiated with the Ne atom current which is linearlydischarged from the outlet 9.

The energy of the plasma which is formed by the ECR ion source 2 is soset that the energy of Ne atoms reaching the substrate 11 is at a valuecausing no sputtering in the Si thin film, i.e., lower than thethreshold energy (=27 eV) in sputtering of Si by irradiation with Neatoms. Therefore, the so-called law of Bravais acts on the amorphous Sithin film as being grown. Namely, the Si atoms in the amorphous Si arerearranged so that a plane which is perpendicular to the direction ofincidence of the Ne atom current applied to the amorphous Si defines thedensest crystal plane, i.e., the (111) plane.

In other words, the amorphous Si thin film being grown by plasma CVD issequentially converted to a-polycrystalline Si thin film in whichdirections of crystal axes perpendicular to a single densest plane areregulated in a direction perpendicular to the surface of the substrate11, i.e., a uniaxially oriented polycrystalline crystalline Si thinfilm. Consequently, a polycrystalline Si thin film is formed on thesubstrate 11, so that a (111) plane is exposed on the surface of anycrystal grain forming this polycrystalline structure.

The diborane gas or the phosphine gas is supplied by the reaction gassupply pipe 13b or 13c simultaneously with the silane gas, therebyforming a p-type or n-type uniaxially oriented polycrystalline Si thinfilm containing B or P.

In the apparatus 122, portions which may be irradiated with the Ne atomcurrent or the Ne ion current before neutralization, such as the innerwall of the reaction vessel 1 and the upper surface of the sample holder10, for example, are made of materials causing no sputtering by theirradiation. In other words, the same are made of materials havinghigher threshold energy values than the energy of the Ne ion current.Therefore, no sputtering is caused in these members by irradiation withthe Ne atom current or the Ne ion current, whereby the thin film isprevented from contamination with material elements forming thesemembers. Further, these members are prevented from damage caused bysputtering.

Since the energy of the Ne ion current is set to be lower than thethreshold energy in the Si thin film to be formed, the reaction vessel1, the sample holder 10 and the like may be made of materials, such asTa, W, Pt and the like shown in Table 2, for example, having thresholdenergy values which are higher than that of the Si thin film in Neirradiation. Alternatively, the surfaces of these members, such as theinner wall of the reaction vessel 1 and the surface of the sample holder10, for example, may be coated with materials such as Ta having highthreshold energy, to obtain a similar effect.

While the structure and the operation of the apparatus 122 have beendescribed with reference to formation of an Si thin film, it is alsopossible to form an axially oriented polycrystalline thin film of amaterial other than Si. For example, it is also possible to form a GaAsthin film. In this case, reaction gases supplied from the reaction gassupply pipes 13a, 13b and 13c are prepared from reaction gasescontaining Ga(CH₃)₃ etc., which are suitable for formation of GaAs.While GaAs is a compound consisting of two elements, an element forforming the ion current or the atom current as applied may be preparedfrom an element such as Ne or Ar, for example, which is lighter than Ashaving larger atomic weight in these two elements. The irradiationenergy is similarly set to be lower than the threshold energy which isrelated to As having large atomic weight.

When the thin film to be formed is made of a plurality of elements, theelement forming the ion current or the atom current as applied may beprepared from that which is lighter than that having the maximum atomicweight among the plurality of elements, in general. The irradiationenergy is similarly set to be lower than threshold energy which isrelated to the element having the maximum atomic weight. In this case,the surface of the member such as the sample holder 10 which isirradiated with the ion current or the atom current in the apparatus 122may be made of a material having higher threshold energy than thematerial for the thin film.

Alternatively, the surface may be made of the same material as the thinfilm. When the apparatus 122 is structured as that for forming anaxially oriented polycrystalline thin film of Si, for example, thesurface of the sample holder 10 etc. may be coated with Si. In thiscase, no contamination of the Si thin film is caused by a differentelement even if sputtering is caused in the sample holder 10 or thelike.

Further, the surface of the member such as the sample holder 10 which isirradiated with the ion current or the atom current may be made of amaterial containing an element which is heavier than that forming theion current or the atom current as applied. In this case, the elementforming the ion current or the atom current hardly penetrates into themember following application of the ion current or the atom current.Thus, deterioration of the member caused by penetration of a differentelement is suppressed.

In the apparatus 122, conversion to a uniaxially orientedpolycrystalline film sequentially progresses simultaneously with growthof the Si thin film by plasma CVD. Thus, it is possible to form anaxially oriented polycrystalline Si thin film having a large filmthickness under a low temperature. Since the axially orientedpolycrystalline thin film can be formed under a low temperature, it ispossible to form a uniaxially oriented crystalline thin film on asubstrate which is already integrated with a prescribed device, forexample, without changing characteristics of this device.

In the above description, the substrate 11 is horizontally placed on thesample holder 10, whereby the atom current is perpendicularly incidentupon the substrate 11. When an axially oriented polycrystalline thinfilm of Si, for example, is formed on the substrate 11, therefore, thesurface of the thin film is defined by a (111) plane. However, it isalso possible to form an axially oriented polycrystalline thin film ofSi in which (111) planes are uniformly oriented in a desired directionwhich is inclined with respect to the surface of the thin film, byplacing the substrate 11 on the sample holder 10 in an inclined manner.

The sample holder 10 may be coupled to a rotary mechanism or the like,to be capable of horizontally rotating the substrate 11. Alternatively,the sample holder 10 may be coupled to a horizontal moving mechanism orthe like, to be capable of horizontally moving the substrate 11. Thus,it is possible to uniformly form a uniaxially oriented thin film on thesubstrate 11.

<A-1-4. Valid Data>

Description is now made on a test verifying formation of an axiallyoriented polycrystalline thin film by the aforementioned method. FIG. 15illustrates experimental data showing an electron beam diffraction imageof a sample comprising an axially oriented polycrystalline Si thin filmformed on a polycrystalline quartz substrate 11 on the basis of theaforementioned method. In this verification test, the surface of thesubstrate 11 was perpendicularly irradiated with an Ne atom current.

As shown in FIG. 15, a diffraction spot appears on a single point, andis continuously distributed along a circumference around the same.Namely, the result of the experiment indicates that a single (111) planeof the Si thin film as formed is oriented to be perpendicular to thedirection of incidence of the atom current, while orientation around thedirection of incidence is arbitrary and not regulated in one direction.Namely, it is verified that this sample is formed as polycrystalline Siin which only a single crystal axis is regulated, i.e., as axiallyoriented polycrystalline Si.

Since it was possible to form an axially oriented polycrystalline Sithin film on the quartz substrate 11 having a polycrystalline structurewhich is higher in regularity in atom arrangement than an amorphousstructure, it can be decided possible to form an axially orientedpolycrystalline thin film on a substrate having an amorphous structureof amorphous Si or the like, as a matter of course. It can also bedecided possible to form an axially oriented polycrystalline thin filmon a substrate having a single-crystalline structure which is equivalentto a structure obtained by enlarging polycrystal grains, similarly tothe above.

<A-6. Fifth Preferred embodiment>

A fifth preferred embodiment of the present invention is now described.

<A-6-1. Overall Structure of Apparatus>

FIG. 16 is a front sectional view showing the overall structure of anapparatus 120 according to the fifth preferred embodiment. Thisapparatus 120 is, similarly to the apparatus 100 shown in FIG. 13, anapparatus for forming single-crystalline thin film which is adapted togrow a thin film of a prescribed material on a substrate and tosimultaneously convert the thin film to a single-crystalline thin film,thereby forming a single-crystalline thin film on the substrate. Thisapparatus 120 is characteristically different from the apparatus 100shown in FIG. 13 in structure of the reflector 12. Furthermore, eachpart of the apparatus 103 is composed of specific materials, asdescribed later.

The reflector 12e is adapted to reflect an atom current which issupplied from an ECR ion source 2, thereby irradiating a substrate 11with the atom current from a plurality of directions. Therefore, thereflector 12e is set to be located immediately under an outlet 9 abovethe substrate 11.

<A-6-2. Structure and Function of Reflector>

FIG. 17 is a perspective view showing a preferable example of thereflector 12e. FIG. 18 is a plan view of the reflector 12e shown in FIG.17, and FIGS. 19 and 20 are exploded views. With reference to thesefigures, the example of the reflector 12e is now described.

This reflector 12e is an exemplary reflector for forming a singlecrystal such as single-crystalline Si, having a diamond structure. Thereflector 12e defines an equilateral hexagonal opening in a centralportion of a flat plate type screen plate 151. Three reflecting blocks153 are fixedly provided on a lower surface of the screen plate 151, toenclose the opening. These reflecting blocks 153 are fastened to thescreen plate 151 by screws passing through holes 157 to be fitted withscrew holes 158. Consequently, an equilateral triangular opening 154which is trimmed with these reflecting blocks 153 is defined immediatelyunder the opening of the screen plate 151.

The atom current which is applied from above is selectively screened bythe screen plate 151, to pass only through the equilateral hexagonalopening. In the reflecting blocks 153, slopes 154 facing the opening 154serve as reflecting surfaces for reflecting the gas beam. As shown inFIG. 18 in a plan view, the three slopes 155 are selectively exposed onthe equilateral hexagonal opening of the screen plate 151 respectively.Therefore, the atom current which is applied from above is divided intofour components in total including a first component passing through theopening 154 to be directly perpendicularly incident upon the substrate11 and second to fourth components reflected by the three slopes 155respectively to be incident upon the substrate 11 from obliquedirections.

As shown in FIG. 18, each of three corners of the equilateral triangularopening 154 coincides with every other corner of the equilateralhexagonal opening, as viewed from above. In other words, the threeslopes 155 are selectively exposed on three isosceles triangles havingadjacent pairs of sides of the equilateral hexagonal opening asisosceles sides. This prevents multiple reflection by the plurality ofslopes 155, while enabling uniform irradiation of the substrate 11 withthe respective atom current components. This is now described withreference to FIGS. 21 and 22.

FIG. 21 is a plan view of the reflector 12e, which is similar to FIG.18. FIG. 22 is a sectional view taken along the line A--A in FIG. 21. Asshown in FIGS. 21 and 22, an atom current which is incident upon aposition (B in the figures) on one slope 155 corresponding to the apexof the equilateral triangle is reflected and then incident upon anopposite apex (C in the figures) of the equilateral triangular opening154. Assuming that D represents an intersection between one side of theopening 154 and the line A--A, an atom current which is applied acrossthe points B and D on the slope 155 is uniformly distributed across thepoints D and C of the opening 154.

This also applies to an atom current which is applied onto an arbitraryline E--E deviating in parallel with the line A--A. Namely, the atomcurrent which is discharged from the outlet 9 is selectively suppliedonto the slopes 155 by the screen plate 151, whereby as-reflected atomcurrents of three components are uniformly incident upon a region of thesubstrate 11 which is located immediately under the opening 154.

Each atom current which is supplied to one slope 155 through theequilateral hexagonal opening is entirely incident upon the opening 154,and is not incident upon the adjacent slope 155. Thus, no componentsmultiplexly reflected by the plurality of slopes 155 are incident uponthe substrate 11.

The angle of inclination of each slope 155 is set at 55°, for example,as shown in FIG. 22. The atom current which is reflected by each slope155 is incident upon the substrate 11 which is located immediately underthe opening 154 at an angle of incidence of 70°. Namely, the firstcomponent is perpendicularly incident upon the substrate 11, while thesecond to fourth components are incident upon the same at angles ofincidence of 70° in directions which are three-fold symmetrical aboutthe direction of incidence of the first component. At this time, thedirections of incidence of the first to fourth components correspond tofour directions which are perpendicular to four (111) planes, beingdensest planes of the Si single crystal.

<A-6-3. Operation of Apparatus>

Referring again to FIG. 16, the operation of the apparatus 120 is nowdescribed. It is assumed that the reflector 12e is prepared from thatshown in FIGS. 17 to 20, and the substrate 11 is prepared frompolycrystalline SiO₂ (quartz), so that a thin film of single-crystallineSi is formed on the quartz substrate 11. It is also assumed that theslopes 155 in the reflector 12e are set at 55°.

Reaction gas supply pipes 13a, 13b and 13c supply SiH₄ (silane) gas forsupplying Si, which is a main material for the single-crystalline Si,and B₂ H₃ (diborane) gas and PH₃ (phosphine) gas for doping thesubstrate 11 with p-type and n-type impurities respectively. Inert gaswhich is introduced from an inert gas inlet pipe 7 is preferablyprepared from Ne gas, which has smaller atomic weight than Si atoms.

Due to the action of an ECR ion generator 2, an Ne⁺ ion current and anelectron current are formed downwardly from the outlet 9. The distancebetween the outlet 9 and the reflector 12e is preferably set at a valuesufficient for converting most part of the Ne⁺ ion current to a neutralNe atom current.

Thus, a plasma CVD reaction progresses on the upper surface of thesubstrate 11 similarly to the apparatus 122 shown in FIG. 13, to grow anamorphous Si thin film. On the other hand, the diborane gas or thephosphine gas is supplied with a properly adjusted flow rate, whereby aplasma CVD reaction caused by this gas also progresses to form the Sithin film containing B (boron) or P (phosphorus) in desired density. .

At the same time, the amorphous Si thin film which is being formed onthe substrate 11 is irradiated with the four components of the Ne atomcurrent, by the action of the reflector 12e. As hereinabove described,directions of incidence of these four components correspond todirections which are perpendicular to four (111) planes of an Si singlecrystal. Similarly to the apparatus 122, further, the energy of plasmawhich is formed by the ECR ion source 2 is so set that the energy of Neatoms reaching the substrate 11 is at a value causing no sputtering inthe Si thin film, i.e., lower than the threshold energy (=27 eV) insputtering of Si by irradiation with Ne atoms. Therefore, the amorphousSi thin film being grown by plasma CVD is sequentially converted to asingle-crystalline Si thin film having a regulated crystal orientation,similarly to the apparatus 100. Consequently, a single-crystalline Sithin film having a regulated crystal orientation is finally formed onthe substrate 11. This single-crystalline Si thin film has a (111) planeon its surface.

In the apparatus 120, due to employment of the reflector 12e, nomultiple reflection of the atom current is caused by the plurality ofslopes 155. Thus, the substrate 11 is irradiated with no atom currentfrom a direction other than the prescribed four directions. Further, thereflector 12e implements uniform irradiation of the substrate 11 withthe atom current, whereby the substrate 11 is uniformly irradiated withthe atom current from the prescribed four directions. Thus, thesingle-crystalline Si thin film is uniformly formed on the substrate 11.

In the apparatus 120, portions which may be irradiated with the Ne atomcurrent or an Ne ion current before neutralization, such as thereflector 12e, the inner wall of the reaction vessel 1 and the sampleholder 10, for example, are made of materials causing no sputtering bythe irradiation, i.e., materials having higher threshold energy valuesthan the energy of the Ne ion current, such as Ta, W, Pt or the likeshown in Table 2, for example. Therefore, no sputtering is caused inthese members by irradiation with the Ne atom current or the Ne ioncurrent, whereby the thin film is prevented from contamination withmaterial elements forming these members.

Alternatively, surfaces of the members irradiated with the Ne atomcurrent such as the upper surface of the screen plate 151 and the slopes155 may be coated with materials such as Ta having high thresholdenergy, to attain a similar effect.

While the structure and the operation of the apparatus 120 have beendescribed with reference to formation of an Si thin film, it is alsopossible to form an axially oriented polycrystalline thin film of amaterial other than Si. For example, it is also possible to form a GaAsthin film. It is possible to form a single-crystalline thin film of anarbitrary material having a desired crystal structure and a desiredcrystal orientation by properly changing the structure of the reflector12e such as the angles of inclination and the number of the slopes 155.The surface of the reflector 12e etc. is made of a material havinghigher threshold energy than that of the thin film.

Alternatively, the surface of the reflector 12e etc. may be made of thesame material as that for the thin film. When the apparatus 120 isstructured as an apparatus for forming a single-crystalline thin film ofSi, for example, the surface of the reflector 12e etc. may be coatedwith Si. In this case, no contamination of the Si thin film is caused bya different element even if sputtering is caused in the reflector 12e orthe like.

Further, the surface of the reflector 12e etc. may be made of a materialcontaining an element which is heavier than that forming the ion currentor the atom current as applied. Thus, the element forming the ioncurrent or the atom current hardly penetrates into the members followingirradiation with the ion current or the atom current. Thus, thesemembers are inhibited from deterioration caused by penetration of thedifferent element.

<A-7. Sixth Preferred Embodiment>

An apparatus according to a sixth preferred embodiment of the presentinvention is now described. FIG. 13 is a front sectional view showingthe overall structure of the apparatus 121 according to this preferredembodiment. This apparatus 121 is, similarly to the apparatus 101 shownin FIG. 4, a single-crystalline thin film forming apparatus, which isadapted to previously form a thin film of a prescribed material havingan amorphous or polycrystalline structure on a substrate and tothereafter convert the thin film to a single-crystalline thin film,thereby forming a single-crystalline thin film on the substrate.

This apparatus 121 is characteristically different from the apparatus101 in structure of the reflector 12e. Furthermore, each part of theapparatus 121 is composed specific materials, as described later. Asample holder 10, which comprises a heater (not shown), can heat asubstrate 11 to hold the same at a proper high temperature.

Referring to FIG. 23, the basic operation of the apparatus 121 is nowdescribed. It is assumed that a reflector 12e is implemented by thatshown in FIGS. 17 to 20 and the substrate 11 is prepared from apolycrystalline quartz substrate, so that a single-crystalline Si thinfilm is formed on the quartz substrate 11. It is also assumed that apolycrystalline Si thin film is previously formed on the quartzsubstrate 11 by a well-known method such as CVD (chemical vapordeposition).

First, the substrate 11 is mounted between the sample holder 10 and thereflector 12e. The heater provided in the sample holder 10 holds thesubstrate 11 at a temperature of 550° C. Since this temperature is lowerthan the crystallization temperature of silicon, single-crystalline Sionce formed will not return to polycrystalline Si under thistemperature. At the same time, this temperature is so high thatpolycrystalline Si can be grown into single-crystalline Si from anuclear of a seed crystal.

For the same reason as that described in relation to the fourthpreferred embodiment, an Ne atom current is selected as an atom currentto be applied to the substrate 11, and energy of Ne plasma which isformed by an ECR ion source 2 is so set that energy of Ne atoms reachingthe substrate 11 is lower than threshold energy in sputtering of Si.Further, the polycrystalline Si thin film which is formed on thesubstrate 11 is irradiated with four components of the Ne atom currentby the action of the reflector 12e. Directions of incidence of thesefour components correspond to those perpendicular to four (111) planesof the Si single crystal.

Therefore, the overall region of the polycrystalline Si thin film isconverted to a single-crystalline Si layer similarly to the apparatus101. Thus, a single-crystalline Si layer having a regulated crystalorientation is formed on the quartz substrate 11.

In the apparatus 121, due to employment of the reflector 12e, nomultiple reflection of the atom current is caused by the plurality ofslopes 155. Thus, the substrate 11 is irradiated with no atom currentfrom a direction other than the prescribed four directions. Further, thereflector 12e implements uniform irradiation of the substrate 11 withthe atom current, whereby the substrate 11 is uniformly irradiated withthe atom current from the prescribed four directions. Thus, thesingle-crystalline Si thin film is uniformly formed on the substrate 11.

Similarly to the apparatus 120, portions which may be irradiated withthe Ne atom current or an Ne ion current before neutralization, such asthe reflector 12e, the inner wall of a reaction vessel 1 and the sampleholder 10, for example, are made of materials causing no sputtering bythe irradiation such as Ta, W, Pt or the like shown in Table 2, forexample, also in the apparatus 121. Therefore, no sputtering is causedin these members by irradiation with the Ne atom current or the Ne ioncurrent, whereby the thin film is prevented from contamination withmaterial elements forming these members.

While the structure and the operation of the apparatus 121 have beendescribed with reference to formation of an Si thin film, it is alsopossible to form an axially oriented polycrystalline thin film of amaterial other than Si with the apparatus 121. For example, it is alsopossible to form a GaAs thin film. Also in this case, the surface of thereflector 12e etc. is made of a material having higher threshold energythan that forming the thin film. Alternatively, the surface of thereflector 12e etc. may be made of the same material as that for the thinfilm, similarly to the apparatus 120. Further, the surface of thereflector 12e etc. may be made of a material containing an element whichis heavier than that forming the ion current or the atom current asapplied.

<A-8. Seventh Preferred Embodiment>

An apparatus according to a seventh preferred embodiment of the presentinvention is now described. FIG. 24 is a front sectional view showingthe overall structure of the apparatus 123 according to this preferredembodiment. This apparatus 123 is an axially oriented polycrystallinethin film forming apparatus which is adapted to previously form a thinfilm of a prescribed material having an amorphous or polycrystallinestructure on a substrate and to thereafter convert the thin film to anaxially oriented polycrystalline thin film, thereby forming an axiallyoriented polycrystalline thin film on the substrate.

As shown in FIG. 24, this apparatus 123 has such a structure that thereflector 12e is removed from the apparatus 121 (FIG. 23). Similarly tothe apparatus 121, a sample holder 10 comprises a heater (not shown),which can heat a substrate 11 to hold the same at a proper hightemperature.

Referring to FIG. 24, the basic operation of the apparatus 123 is nowdescribed. It is assumed that the substrate 11 is prepared from apolycrystalline quartz substrate, so that an axially orientedpolycrystalline Si thin film is formed on the quartz substrate 11. It isalso assumed that a polycrystalline Si thin film is previously formed onthe quartz substrate 11 by a well-known method such as CVD (chemicalvapor deposition). This polycrystalline Si thin film may have such anordinary polycrystalline structure that respective crystal grains areoriented in arbitrary directions.

First, the substrate 11 is mounted on the sample holder 10. The heaterprovided in the sample holder 10 holds the substrate 11 at a temperatureof 550° C. Since this temperature is lower than the crystallizationtemperature of silicon, axially oriented polycrystalline Si once formedwill not return to ordinary polycrystalline Si under this temperature.At the same time, this temperature is so high that ordinarypolycrystalline Si can be grown into axially oriented polycrystalline Sifrom a nuclear of a seed crystal.

An ion current passing through an outlet 9 is converted to an atomcurrent, which in turn is perpendicularly incident upon the surface ofthe substrate 11. For the same reason as that described in relation tothe seventh preferred embodiment, an Ne atom current is selected as theatom current to be applied to the substrate 11, and energy of Ne plasmawhich is formed by an ECR ion source 2 is so set that energy of Ne atomsreaching the substrate 11 is lower than threshold energy in sputteringof Si.

Thus, the law of Bravais acts in a portion close to the surface of thepolycrystalline Si thin film, whereby the Si atoms are rearranged in aportion close to the surface of the polycrystalline Si thin film so thata surface perpendicular to the direction of incidence of the Ne atomcurrent which is applied to the polycrystalline Si thin film defines thedensest crystal plane. Namely, a layer close to the surface of thepolycrystalline Si tin film is converted to an axially orientedpolycrystalline Si layer whose uniaxial direction is regulated so thatthe (111) plane is along its surface.

The temperature of the polycrystalline Si thin film is adjusted at 550°,i.e., within a range suitable for growing a seed crystal, as describedabove. Thus, the axially oriented polycrystalline Si layer which isformed on the surface of the ordinary polycrystalline Si thin filmserves as a seed crystal, to grow the axially oriented polycrystallineSi layer toward a deep portion of the ordinary polycrystalline Si thinfilm. Then, the overall region of the polycrystalline Si thin film isconverted to an axially oriented polycrystalline Si layer. Thus, anaxially oriented polycrystalline Si layer which is so oriented that the(111) plane is along its surface is formed on the quartz substrate 11.

Alternatively, an amorphous Si thin film may be previously formed on thesubstrate 11 in place of the ordinary polycrystalline Si thin film to bethereafter treated with the apparatus 123, thereby forming an axiallyoriented polycrystalline Si thin film.

Also in the apparatus 123, portions which may be irradiated with the Neatom current or an Ne ion current before neutralization, such as atleast surfaces of the inner wall of a reaction vessel 1 and the sampleholder 10, for example, are made of materials causing no sputtering bythe irradiation, such as Ta, W, Pt or the like shown in Table 2, forexample, similarly to the apparatus 122. Therefore, no sputtering iscaused in these members by irradiation with the Ne atom current or theNe ion current, whereby the thin film is prevented from contaminationwith material elements forming these members.

While the structure and the operation of the apparatus 123 have beendescribed with reference to formation of an Si thin film, it is alsopossible to form an axially oriented polycrystalline thin film of amaterial other than Si by the apparatus 123. For example, it is alsopossible to form a GaAs thin film. Also in this case, the surface of thesample holder 10 etc. is made of a material having higher thresholdenergy than that of the thin film. Alternatively, the surface of thesample holder 10 etc. may be made of the same material as that for thethin film, similarly to the apparatus 122. Further, the surface of thesample holder 10 etc. may be made of a material containing an elementwhich is heavier than that forming the ion current or the atom currentas applied.

<A-9. Eighth Preferred Embodiment>

An eighth preferred embodiment of the present invention is nowdescribed. A method according to this preferred embodiment is adapted toform an axially oriented polycrystalline thin film on a substrate 11 andto thereafter convert the same to a single-crystalline thin film byirradiating the film with atom currents from a plurality of directions,thereby forming a single-crystalline thin film on the substrate 11. Tothis end, the apparatus 122 according to the fourth preferred embodimentmay be employed to form an axially oriented polycrystalline thin film onthe substrate 11, so that this thin film is converted to asingle-crystalline thin film through the apparatus 121 according to theseventh preferred embodiment, for example.

Alternatively, the apparatus 120 according to the eighth preferredembodiment may be employed to form an axially oriented polycrystallinethin film by executing supply of reaction gas and application of an atomcurrent at first while removing the reflector 12e, so that the reflector12e is thereafter set in the apparatus 120 to execute application of anatom current while heating the substrate 11 for converting the thin filmto a single-crystalline thin film, thereby forming a single-crystallinethin film on the substrate 11.

Alternatively, a thin film having an amorphous structure or an ordinarypolycrystalline structure may be previously formed on the substrate 11by CVD or the like so that the thin film is thereafter converted to anaxially oriented polycrystalline thin film through the apparatus 123 andthereafter the film is further converted to a single-crystalline thinfilm through the apparatus 121, thereby forming a single-crystallinethin film on the substrate 11.

Thus, in the method according to this preferred embodiment, an axiallyoriented polycrystalline thin film is previously formed before asingle-crystalline thin film is formed on the substrate 11. Even if aportion which is hard to form a single-crystalline thin film is presenton the substrate 11, therefore, mechanical and electrical properties ofthe thin film are not remarkably deteriorated since the portion isprovided with an axially oriented polycrystalline thin film havingcharacteristics which are close to those of a single-crystalline thinfilm. Namely, it is possible to obtain a thin film having properlyexcellent characteristics without precisely executing a step of forminga single-crystalline thin film.

This is particularly effective when it is difficult to uniformlyirradiate a prescribed region of the substrate 11 with atom currentsfrom a plurality of directions since the substrate 11 is not in the formof a flat plate but is in the form of a cube, or a screen having athickness is formed on the surface of the substrate 11. FIGS. 25 to 27show such examples.

FIG. 25 is a sectional view typically illustrating such a state that thesurface of a sample 170 comprising a substrate 11 having a cubic shapeand an axially oriented polycrystalline Si thin film 171 previouslyformed thereon is irradiated with Ne atom currents from two directions.As shown in FIG. 25, the sample 170 has a cubic shape and hence thesample 170 itself serves as a screen for the atom currents.Consequently, a specific region of the axially oriented polycrystallineSi thin film 171 is irradiated with the Ne atom current from only onedirection, and no irradiation from two directions is implemented.

FIGS. 26 and 27 are sectional views typically showing steps ofselectively forming a single-crystalline Si thin film on a substrate 11through a masking member 172 in a process of fabricating a thin-filmsemiconductor integrated circuit. An amorphous or ordinarypolycrystalline Si thin film 174 is previously formed on the substrate11 by CVD or the like. Thereafter the apparatus 123 is employed toperpendicularly irradiate the upper surface of the Si thin film 174 withan Ne atom current through an opening of the masking member 172 which ismade of SiO₂ or the like, thereby selectively forming an axiallyoriented polycrystalline Si thin film 171 immediately under the openingof the masking member 172 (FIG. 26).

Then, the apparatus 121 is employed to irradiate the upper surface ofthe Si thin film 171 with Ne atom currents from a plurality ofdirections through the opening of the masking member 172, therebyconverting the axially oriented polycrystalline Si thin film 171 to asingle-crystalline Si thin film (FIG. 27). At this time, a portion closeto an edge of the opening of the masking member 172 is not sufficientlyirradiated with the Ne atom currents from the plurality of directionssince the masking member 172 has a constant thickness. Thus, thesingle-crystalline Si thin film is hardly formed in the portion close tothe edge of the opening of the masking member 172. However, at least theaxially oriented polycrystalline Si thin film is provided in thisportion even if no single-crystalline Si thin film is formed, whereby itis possible to minimize deterioration of electrical properties such ascarrier mobility.

In the method according to this preferred embodiment, one of theplurality of directions of incidence of the atom currents which areapplied to carry out conversion to a single-crystalline thin film ispreferably coincident with the direction of incidence of the atomcurrent which is applied in advance for forming the axially orientedpolycrystalline thin film. In this case, conversion to asingle-crystalline thin film is carried out without changing the commonuniaxial direction in the axially oriented polycrystalline thin film,whereby the step of conversion to a single-crystalline thin filmsmoothly progresses in a short time.

<A-10. Ninth Preferred Embodiment>

A ninth preferred embodiment of the present invention is now described.

<A-10-1. Structure of Apparatus>

FIG. 28 is a front sectional view showing the overall structure of anapparatus 124 according to this preferred embodiment. This apparatus 124is adapted to convert an amorphous, polycrystalline, or axially orientedpolycrystalline thin film which is previously formed on a substrate 11to a single-crystalline thin film, thereby forming a single-crystallinethin film on the substrate 11.

This apparatus 124 is characteristically different from the apparatus121 in a point that a reflecting unit 160 is set in place of thereflector 12e. The reflecting unit 160, which is adapted to generate aplurality of atom current components to be incident upon the substrate11 at a plurality of prescribed angles of incidence, is set on a sampleholder 10, to be located above the substrate 11. The sample holder 10comprises a heater (not shown), which can heat the substrate 11 tomaintain the same at a proper high temperature.

<A-10-2. Structure and Operation of Reflecting Unit>

The structure and the operation of the reflecting unit 160 are nowdescribed. FIGS. 29 and 30 are a front sectional view and a plansectional view showing the structure of the reflecting unit 160respectively. The reflecting unit 160 illustrated in FIGS. 29 and 30 isadapted to form a single crystal of a diamond structure such assingle-crystalline Si. This reflecting unit 160 is arranged directlyunder an ion outlet 9 of an ECR ion source 2, i.e., downstream an atomcurrent which is generated by the ECR ion source 2 to be downwardlydirected.

A screen plate 164 which can selectively screen the atom currentsupplied from the ECR ion source 2 is horizontally provided on an upperportion of the reflecting unit 160. The reflecting unit 160 is so setthat a distance between the outlet 9 and this screen plate 164 is at asufficient value, such as at least 14 cm, for example, for converting anion current outputted from the ECR ion source 2 to a neutral atomcurrent. Namely, a substantially neutral atom current reaches the screenplate 164. Openings 162 are provided in this screen plate 164, to be infour-fold rotation symmetry about a central axis of the atom currentfrom the ECR ion source 2. The atom current from the ECR ion source 2passes only through the openings 162, to further flow downwardly.

A reflecting block 166 is set immediately under this screen plate 164.This reflecting block 166 is in the form of a four-foldrotary-symmetrical cone whose symmetry axis is coincident with thecentral axis of the atom current, and four side surfaces of the cone arelocated immediately under the four openings 162 respectively. These sidesurfaces are not necessarily plane, but are curved in general. Thesefour side surfaces serve as reflecting surfaces for reflecting the atomcurrent. Namely, the atom current passing through the openings 162 isreflected by the four side surfaces of the reflecting block 166, wherebyfour atom current components progressing toward directions separatedfrom the central axis are obtained.

These four atom current components are divergent beams whose beamsections are two-dimensionally (planarly) enlarged. These fourcomponents pass through a rectifying member (rectifying means) 168 sothat directions of progress thereof are accurately regulated in desireddirections, to be thereafter incident upon four reflectors 169respectively. The rectifying member 168, which is adapted to regulatethe directions of the atom current components radially from the sidesurfaces of the reflecting block 166 toward the reflecting plates 169,can be formed by a well-known technique.

These four reflectors 169 are arranged around the substrate 11, which isthe target of irradiation, to be four-fold rotation symmetrical aboutthe symmetry axis of the reflecting block 166 (FIG. 30 typically showsonly one reflector 169. FIG. 30 also illustrates only an atom currentwhich is incident upon and reflected by an upper half portion of thesingle reflector 169). The atom current component which is incident uponeach reflector 169 is again reflected by its reflecting surface. Thereflecting surface of each reflector 169 has a shape of a proper concavesurface. Therefore, the divergent atom current components are reflectedby the reflecting surfaces and properly focused as the result, to formparallel beams which are uniformly applied to the overall upper surfaceof the substrate 11. Further, the parallel beams are incident upon theupper surface of the substrate 11 from four directions at angles ofincidence of 55°, for example.

<A-10-3. Operation of Apparatus 124>

Referring to FIG. 28, the operation of the apparatus 124 is nowdescribed. It is assumed that the substrate 11 is prepared from anamorphous or polycrystalline SiO₂ (quartz) substrate, so that asingle-crystalline Si thin film (which includes an axially orientedpolycrystalline Si thin film) is formed on the quartz substrate 11. Apolycrystalline Si thin film is previously formed on the quartzsubstrate 11 by CVD (chemical vapor deposition), for example.

First, the substrate 11 is mounted between the sample holder 10 and thereflecting unit 160. The heater provided in the sample holder 10 holdsthe sample, i.e., the substrate 11 and the polycrystalline Si thin film,at a temperature of 550° C. Similarly to the apparatus 121, a gas whichis introduced from an inert gas inlet pipe 7 is preferably prepared frominert Ne gas having smaller atomic weight than Si atoms.

Due to the action of an ECR ion source 2, an Ne atom current is suppliedto the reflecting unit 160, to be incident upon the overall uppersurface of the substrate 11 from four directions at angles of incidenceof 55°, for example. In this case, the directions of incidence of thefour Ne atom current components correspond to four directions which areperpendicular to four independent densest crystal planes of an Si singlecrystal to be formed, i.e., (111) planes. Similarly to the apparatus121, energy of plasma which is formed by the ECR ion source 2 is so setthat energy of the Ne atoms reaching the substrate 11 is lower thanthreshold energy in sputtering of Si by irradiation with the Ne atoms.

Thus, the law of Bravais acts on the polycrystalline Si thin film,whereby the Si atoms are rearranged in a portion close to the surface ofthe polycrystalline Si thin film so that surfaces perpendicular to thedirections of incidence of the four components of the Ne atom currentwhich is applied to the polycrystalline Si thin film define densestcrystal planes. Namely, a layer in the vicinity of the polycrystallineSi thin film is converted to a single-crystalline Si layer having aregulated crystal orientation.

The temperature of the polycrystalline Si thin film is adjusted at 550°,i.e., within a range suitable for growing a seed crystal, as describedabove. Thus, the single-crystalline Si layer which is formed on thesurface of the polycrystalline Si thin film serves as a seed crystal, togrow the single-crystalline Si layer toward a deep portion of thepolycrystalline Si thin film. After a lapse of a constant time, theoverall region of the polycrystalline Si thin film is converted to asingle-crystalline Si layer. Thus, a single-crystalline Si layer havinga regulated crystal orientation is formed on the quartz substrate 11.The single-crystalline Si thin film as formed is so oriented that the(100) plane is along its surface.

The angle of incidence of 55° shown in FIG. 29 is a mere example as amatter of course, and it is possible to introduce parallel beams intothe substrate 11 at an arbitrary angle of incidence which is decided inresponse to the crystal structure of the desired single-crystalline thinfilm by properly changing the shapes and directions of the reflectors169. Since the divergent beams are generated by the reflecting block166, it is possible to uniformly irradiate a wide substrate 11 withparallel beams by properly adjusting the distances between thereflectors 169 and the symmetry axis of the reflecting block 166 inresponse to the width of the substrate 11.

Thus, according to this apparatus 124, it is possible to uniformlyirradiate the overall surface of the substrate 11 having an area whichis extremely larger than the section of each beam supplied from the ECRion source 2 with atom current components at desired angles ofincidence. Namely, it is possible to uniformly and efficiently form adesired single-crystalline thin film on the substrate 11 having a largearea.

Further, it is possible to independently adjust the amounts of the fourcomponent beams passing through the openings 162 by independentlyadjusting the areas of the four openings 162 provided in the screenplate 164. Thus, it is possible to optimumly set the respective amountsof the four component beams which are applied to the upper surface ofthe substrate 11 from a plurality of directions. For example, it ispossible to uniformly regulate the amounts of the four component beams.Thus, a high-quality single-crystalline thin film can be efficientlyformed.

Similarly to the apparatus 121, at least surfaces of respective membersof the reflecting unit 160 such as the reflecting block 168, therectifying member 168 and the reflectors 169 which are irradiated withthe atom current components may be made of materials such as Ta, W, Ptor the like having higher threshold energy in sputtering than the thinfilm to be formed. Alternatively, the surfaces of the respective membersof the reflecting unit 160 may be made of the same material as that forthe thin film, similarly to the apparatus 121. Further, the surfaces ofthe respective members of the reflecting unit 160 may be made of amaterial containing an element which is heavier than that forming theion current or the atom current as applied.

<A-11. Tenth Preferred Embodiment>

An apparatus according to a tenth preferred embodiment of the presentinvention is now described. FIG. 31 is a front sectional view showingthe overall structure of a beam irradiator according to this preferredembodiment. This apparatus 125 is adapted to form a polycrystalline thinfilm on a substrate 11 and to irradiate the same with an atom current atthe same time, thereby sequentially converting the polycrystalline thinfilm as being grown to a single-crystalline thin film, similarly to theapparatus 120.

To this end, a reaction chamber 8 communicates with reaction gas supplypipes 13 in the apparatus 125, similarly to the apparatus 120. Reactiongases are supplied through the reaction gas supply pipes 13, for forminga film of a prescribed material on the substrate 11 by plasma CVD. Thepreferred embodiment shown in FIG. 31 is provided with three reactiongas supply pipes 13a, 13b and 13c. Other structural characteristics ofthis apparatus 125 are similar to those of the apparatus 124.

The apparatus 125 operates as follows: Similarly to the sixth preferredembodiment, it is assumed that the substrate 11 is prepared frompolycrystalline SiO₂ (quartz), so that a thin film of single-crystallineSi is formed on the quartz substrate 11. The reaction gas supply pipes13a, 13b and 13c supply SiH₄ (silane) gas for supplying Si, which is amain material for the single-crystalline Si, and B₂ H₃ (diborane) gasand PH₃ (phosphine) gas for doping the substrate 11 with p-type andn-type impurities respectively. Ne gas is introduced from an inert gasinlet pipe 7 into a plasma chamber 4.

Due to the reaction gases supplied from the reaction gas supply pipes13a, 13b and 13c and an Ne⁺ ion current or an Ne atom current generatedby an ECR ion source 2, plasma CVD reaction progresses on the uppersurface of the substrate 11, thereby growing an Si thin film of anamorphous structure.

The Ne atom current downwardly flowing from the ECR ion source 2 isincident upon the overall surface of the Si thin film being formed onthe upper surface of the substrate 11 from four directions having anglesof incidence of 55°, for example, due to action of a reflecting unit160. Similarly to the apparatus 120, energy of plasma which is formed bythe ECR ion source 2 is so set that incident energy of the fourcomponents is lower than threshold energy with respect to Si. Thus, thelaw of Bravais acts on the amorphous Si thin film as being grown,whereby the amorphous Si thin film being grown by plasma CVD issequentially converted to a single-crystalline Si thin film having aregulated crystal orientation. As the result, single-crystalline Sihaving a single crystal orientation is formed on the substrate 11.

Also in this apparatus 125, the reflecting unit 160 is so employed thatit is possible to uniformly irradiate the overall surface of thesubstrate 11 having an area which is extremely larger than the sectionof each beam supplied from the ECR ion source 2 with atom currentcomponents at desired angles of incidence without scanning the substrate11, due to employment of the reflecting unit 160. Namely, it is possibleto uniformly and efficiently form a desired single-crystalline thin filmon the substrate 11 having a large area.

<A-12. Eleventh Preferred Embodiment>

An apparatus 126 according to an eleventh preferred embodiment of thepresent invention is now described. FIGS. 32 to 34 are a perspectiveview, a plan view and a front elevational view showing the apparatus 126according to this preferred embodiment respectively. With reference toFIGS. 32 to 34, the structure and the operation of the apparatus 126according to this preferred embodiment are now described.

In this apparatus 126, an ECR ion source 2 is set in a horizontal state,to supply a gas beam in a horizontal direction which is parallel to thesurface of a horizontally set substrate 11. A reflecting unit 180 isinterposed in a path of the gas beam which is supplied from the ECR ionsource 2 to reach the upper surface of the substrate 11.

In the reflecting unit 180, a reflecting block 186, a screen plate 184,a rectifying member 188 and a reflector 190 are successively arrangedalong the path of the gas beam. The reflecting block 186 isrotated/driven about its central axis which is in the form of aperpendicular prism. A distance between an outlet 9 and the reflectingblock 186 is set at a sufficient length of at least 14 cm, for example,for converting an ion current which is outputted from the ECR ion source2 to a neutral atom current. Thus, a substantially neutral atom currentreaches the reflecting block 186.

FIG. 35 is a plan view for illustrating the operation of the reflectingblock 186. As shown in FIG. 35, an atom current which is incident uponthe reflecting block 186 is scattered to a number of directions in ahorizontal plane by rotation of the reflecting block 186. Namely, thereflecting block 186 substantially generates divergent beams whose beamsections are enlarged linearly or in the form of strips, i.e.,substantially one-dimensionally, with progress of the beams.

The screen plate 184 selectively passes only components of the divergentatom current having scattering angles in a specific range. The atomcurrent components passed through the screen plate 184 are passedthrough the rectifying member 188, to be precisely regulated indirections of progress. The rectifying member 188 is structuredsimilarly to the rectifying member 168. In place of the shape of a prismshown in FIG. 35, the reflecting block 186 may be in the form of atriangle pole, a hexagonal pole or the like, for example.

Referring again to FIGS. 32 to 34, the atom current components passedthrough the rectifying member 188 are incident upon the reflector 190which is in the form of a strip along the horizontal direction. Areflecting surface of the reflector 190 has a proper concave shape.Thus, the divergent atom current components are reflected by thisreflecting surface and properly focused to form parallel beams, whichare applied to the upper surface of the substrate 11 linearly or in theform of strips. Further, the parallel beams are incident upon the uppersurface of the substrate 11 at angles of incidence of 35°, for example.As shown in FIG. 33, two sets of the members from the reflecting block186 to the reflector 190 arranged along the path of the atom current areset. Thus, atom currents are incident upon the substrate 11 fromopposite two directions at angles of incidence of 35° respectively.

Each atom current is scattered by each reflecting block 186 to besubstantially one-dimensionally diverged, whereby it is possible toapply parallel beams to a linear or strip-shaped region having a widthwhich is extremely larger than the diameter of the beam supplied fromthe ECR ion source 2 by sufficiently setting the distance between thereflecting block 186 and the reflector 190.

The apparatus 126 has a sample holder (not shown) for receiving thesubstrate 11, and this sample holder is horizontally movable by ahorizontal moving mechanism (not shown). Following such horizontalmovement of the sample holder, the substrate 11 is moved in parallelalong a direction perpendicular to (intersecting with) the linear orstrip-shaped region receiving the atom currents. Thus, it is possible toimplement irradiation of the overall region of the substrate 11 byscanning the substrate 11. Due to such scanning of the substrate 11, itis possible to uniformly irradiate the wide substrate 11 with atomcurrent components.

This apparatus 126 may comprise reaction gas supply pipes 13a, 13b and13c similarly to the apparatus 120, to form a thin film of a prescribedmaterial on the substrate 11 and to sequentially convert the thin filmto a single crystal. Alternatively, the sample holder may be providedwith a heater similarly to the apparatus 121, to convert a thin film ofa prescribed material which is previously deposited on the substrate 11to a single-crystalline thin film. Since the two atom currents areincident from opposite directions at the same angles of incidence of35°, the single-crystalline thin film formed on the substrate 11 is sooriented that its (110) plane is along its surface.

It is possible to form a single-crystalline thin film which is sooriented that a crystal plane other than the (110) plane is along itssurface, by changing the positional relation between the reflectingunits 180, the angles of the reflectors 190 and the like. For example,it is possible to form a single-crystalline thin film which is sooriented that its (100) plane is along its surface by arranging at leasttwo sets of reflecting units 180 so that central axes of atom currentsfrom the reflecting blocks 186 toward the reflectors 190 are at anglesof 90° or 180° and setting shapes and directions of the reflectors 190so that angles of incidence of the atom currents incident upon thesubstrate 11 from the reflecting units 180 are 55°.

Further, it is possible to form a single-crystalline thin film which isso oriented that its (111) plane is along its surface by arranging atleast two sets of three sets of of reflecting units 180 so that centralaxes of atom currents from the reflecting blocks 186 toward thereflectors 190 are each shifted by 120° and setting shapes anddirections of the reflectors 190 so that angles of incidence of the atomcurrents incident upon the substrate 11 from the reflecting units 180are at 70°.

Similarly to the apparatus 124, at least surfaces of respective membersof the reflecting units 160 such as the reflecting blocks 168, therectifying members 168 and the reflectors 169 which are irradiated withthe atom current components may be made of materials such as Ta, W, Ptor the like having higher threshold energy in sputtering than the thinfilm to be formed. Alternatively, the surfaces of the respective membersof the reflecting units 160 may be made of the same material as that forthe thin film. Further, the surface of the respective members of thereflecting units 160 may be made of a material containing an elementwhich is heavier than that forming the ion current or the atom currentas applied.

<A-13. Twelfth Preferred Embodiment>

An apparatus 127 according to a twelfth preferred embodiment of thepresent invention is now described. FIG. 36 is a perspective viewshowing the structure of the apparatus 127 according to this preferredembodiment. As shown in FIG. 36, this apparatus 127 comprises areflecting unit 191. This reflecting unit 191 is characteristicallydifferent from the reflecting unit 180 in a point that the same has anelectrostatic electrode 306 in place of the reflecting blocks 186. Anion current is incident upon the electrostatic electrode 196, in placeof a neutral atom current. Namely, a distance between an outlet 9 andthis electrostatic electrode 196 is set to be sufficiently short so thatthe ion current outputted from an ECR ion source 2 is hardly convertedto a neutral atom current but incident upon the electrostatic electrode196 as such.

The electrostatic electrode 196 is provided with an ac power source 197.This ac power source 197 supplies a fluctuation voltage which is formedby an alternating voltage superposed on a constant bias voltage to theelectrostatic electrode 196. Consequently, the ion current which isincident upon the electrostatic electrode 196 is scattered into a numberof directions within a horizontal plane by action of a fluctuatingelectrostatic field.

Thus, scattering of the ion current is implemented by the fluctuationvoltage which is supplied by the ac power source 197 in this apparatus127, whereby it is possible to easily suppress scattering of the ioncurrent in unnecessary directions cut by screen plates 184. Namely, itis possible to efficiently apply the ion current which is supplied bythe ECR ion source 2 to a substrate 11. Further, it is also possible toscatter the ion current to respective scattering directions with higheruniformity by setting the waveform of the fluctuation voltage suppliedby the ac power source 197 in the form of a chopping wave, for example.

<A-14. Modifications of Fifth to Twelfth Preferred Embodiments>

(1) While the shapes of the reflecting blocks 166 and the arrangement ofthe reflectors 169 are selected to four-fold rotation symmetry in thesixth and tenth preferred embodiments, the same can alternatively beselected in two-fold or three-fold rotation symmetry, for example.Namely, it is possible to arbitrarily select the number of components ofthe atom current which are incident at different angles of incidence inresponse to the crystal structure of the desired single-crystalline thinfilm. The shape of the reflecting block 166 may be selected in arotation symmetrical manner such as in the form of a cone. At this time,only a single reflecting block 166 is available regardless of the numberof the directions of incidence upon the substrate 11. Thus, it is alsopossible to form a single-crystalline thin film having a crystalstructure other than a diamond structure according to the inventiveapparatus, while it is also possible to form a single-crystalline thinfilm having various crystal orientations in a single crystal structure.Further, the material for forming the single-crystalline thin film isnot restricted to Si since it is possible to cope with an arbitrarycrystal structure, whereby it is possible to form a semiconductorsingle-crystalline thin film of GaAs or GaN, for example.

(2) In each of the ninth and tenth preferred embodiments, eachrectifying member 168 for rectifying the directions of the atom currentcomponents may be interposed in a path of the atom current which isreflected by the reflector 169 and directed toward the substrate 11, inplace of the path of the atom current directed from the reflecting block166 toward the reflector 169. Further, the rectifying members 168 may beinterposed in both of these paths.

On the other hand, the apparatus may not be provided with the rectifyingmembers 168. When the apparatus is provided with the rectifying members168, however, it is possible to precisely set the directions ofincidence of the atom current components upon the substrate 11 withoutstrictly setting the shapes, arrangement etc. of the reflecting blocks166 and the reflectors 169.

The above also applies to the rectifying members 188 in the eleventh andtwelfth preferred embodiments.

(3) In each of the fourth to eleventh preferred embodiments, the ECR ionsource 2 may be replaced by another beam source for generating a neutralatom current or a neutral molecular flow, or a neutral radical flow. Abeam source for generating such a neutral atom or radical current hasalready been commerciall available. Since a neutral atom or radical beamcan be obtained by such a beam source, it is possible to form asingle-crystalline thin film on an insulating substrate 11 with norequirement for means for neutralizing an ion current, similarly to thecase of employing the ECR ion source 2.

(4) In each of the fourth to twelfth preferred embodiments, the ECR ionsource 2 may be replaced by another ion source such as a Cage type orKaufmann type source. In this case, however, the flow of theas-generated ion current may be diffused by repulsive force by staticelectricity between ions to be weakened in directivity, and hence meansfor neutralizing the ions or means such as a collimator for improvingdirectivity of the ion current is preferably interposed in the path ofthe ion current.

Particularly when the substrate 11 is made of an electrically insulatingmaterial, means for neutralizing ions is preferably interposed in thepath of the ion current, in order to prevent the substrate 11 fromaccumulation of electric charges inhibiting progress of irradiation. Inthe apparatus according to each preferred embodiment comprising the ECRion source 2, on the other hand, a neutral atom current can be easilyobtained in a shape close to a parallel current with no means forneutralizing the ion current.

When means for neutralizing ions is set in the apparatus according tothe twelfth preferred embodiment, the same is set downstream theelectrostatic electrode 196.

(5) The beam irradiator described in each of the aforementionedpreferred embodiments is not restricted to an apparatus for forming asingle-crystalline thin film, but is also applicable to an apparatus forapplying gas beams from a plurality of directions for another purpose.Particularly the apparatus shown in each of the ninth to twelfthpreferred embodiments is suitable for a purpose of uniformly irradiatinga wide substrate with gas beams from a plurality of directions.

(6) When the thin film to be formed contains N (nitrogen element) whichis a gas under a normal temperature such as GaN in each of the fourth totwelfth preferred embodiments, the gas may be prepared from gaseousnitrogen. In this case, the characteristics of the thin film will not bedeteriorated even if the gas remains in the thin film.

<B. Preferred embodiments in Relation to Selective Formation and FurtherEfficient Formation of Single-Crystalline Thin Film>

On the basis of the aforementioned method, description is now made onpreferred embodiments in relation to methods enabling selectiveformation of single-crystalline thin films on specific regions ofsubstrates and further efficient formation of single-crystalline thinfilms on substrates.

<B-1. Thirteenth Preferred embodiment>

FIGS. 37 to 42 are process diagrams in relation to a method according toa thirteenth preferred embodiment. First, an upper surface of an Sisingle-crystalline substrate 102 is oxidized to form an SiO₂ film 104which is an insulator, as shown in FIG. 37. Further, an amorphous orpolycrystalline Si thin film 106 is formed on the SiO₂ film 104 by CVD,for example.

Then, a thin film 108 of SiO₂ or Si₃ N₄ is formed on the Si thin film106 and thereafter this thin film 108 is selectively etched to form anopening in a desired specific region, as shown in FIG. 38. This thinfilm 108 having an opening serves as a masking material in a subsequentstep. The selective etching is carried out by well-knownphotolithography sequentially through processes of resist application,pre-baking, exposure, development and post-baking. At this time, theexposure is carried out through a masking material having a prescribedpattern enabling selective etching, and separation of a resist materialis carried out after the exposure. A portion of the Si thin film 106which is exposed in the opening is subjected to washing by a method suchas the so-called reverse sputtering or the like.

Thereafter the apparatus 101 is employed to irradiate the overall uppersurface of the Si single-crystalline substrate 102 with an Ne atomcurrent 110 from directions which are perpendicular to a plurality ofdensest planes of a single-crystalline thin film to be formed withproper irradiation energy, as shown in FIG. 39. Ne atoms are lighterthan Si which is an element forming the Si thin film 106 as irradiatedand Si which has the maximum atomic weight among elements forming themasking material 108 as irradiated, whereby the same hardly remain inthe masking material 108 and the Si thin film 106 following theirradiation.

The Si thin film 106 is selectively irradiated with the Ne atom currentonly in the opening of the masking material 108. Therefore, the Si thinfilm 106 is selectively converted to a single-crystalline layer 112having a regulated crystal orientation in a region corresponding to theopening of the masking material 108, i.e., the aforementioned specificregion, as shown in FIG. 40.

Then, the masking material 108 is remove and the upper surface isthermally oxidized to form an oxide film 114, as shown in FIG. 41. Ingeneral, a reaction rate of thermal oxidation in an amorphous orpolycrystalline layer is larger by 2 to 5 times than that in asingle-crystalline layer. Therefore, a portion of the oxide film 114located on the Si thin film 106 is larger in thickness by about 2 to 5times than that located on the single-crystalline layer 112.

Thereafter the overall upper surface of the oxide film 114 is properlyetched to expose the upper surface of the single-crystalline layer 112,as shown in FIG. 42. At this time, the oxide film 116 remains on the Sithin film 106. The single-crystalline layer 112 can be provided with adesired element such as a transistor element, for example. At this time,the oxide film 116 serves as the so-called LOCOS (local oxidation ofsilicon) layer which isolates the element formed on thesingle-crystalline layer 112 from other elements. The Sisingle-crystalline substrate 102 itself is already provided therein withdesired elements. Therefore, it is possible to implement a device havinga three-dimensional structure by integrating a new element into thesingle-crystalline layer 112. In the method according to this preferredembodiment, the LOCOS layer is formed on an amorphous or polycrystallinelayer, whereby the same can be efficiently formed in a short time, toimprove the throughput in an thermal oxidation device.

In the method according to this preferred embodiment, further, asingle-crystalline thin film can be formed on the SiO₂ film 104 which isan insulator, whereby the element provided in the Si single-crystallinesubstrate 102 can be easily isolated from a new element providedthereon.

<B-2. Fourteenth Preferred embodiment>

FIGS. 43 to 51 are process diagrams in relation to a fourteenthpreferred embodiment. As shown in FIG. 43, a transistor is previouslyformed on a single-crystalline Si substrate. Namely, n-type source anddrain layers 204 and 206 which are isolated from each other areselectively formed on an upper surface of a p-type single-crystalline Sisubstrate 202. Further, a gate electrode 210 is formed on the uppersurface of the substrate 202 in a region corresponding to that betweenthese layers 204 and 206, through a gate oxide film 208. Namely, thistransistor is an n-channel MOS transistor. The gate oxide film 208 ismade of SiO₂, and the gate electrode 210 is made of polycrystalline Si.

Then, an insulating film 212 of SiO₂ is formed entirely over the uppersurfaces of the substrate 202 and the gate electrode 210, as shown inFIG. 44. Thereafter an amorphous or polycrystalline Si film 214 isformed on the overall surface of the insulating film 212, as shown inFIG. 45.

Then, the Si film 214 is selectively etched to be left only in a desiredspecific region. FIG. 46 shows an Si film 216 which is defined in thespecific region by the selective etching.

Then, the apparatus 101 is employed to irradiate overall upper surfacesof the insulating film 212 and the Si film 216 with an Ne atom current218 from directions which are perpendicular to a plurality of densestplanes of a single-crystalline thin film to be formed with properirradiation energy, as shown in FIG. 47. Ne atoms are lighter than Siforming the Si film 216 and the insulating film 212, whereby the samehardly remain in these layers following the irradiation. Due to thisirradiation, the Si film 216 is converted to a single-crystalline Sithin film 220 having a regulated crystal orientation, as shown in FIG.48. At this time, a region of the insulating film 212 which is exposedon the upper surface is also converted to a single-crystalline thinfilm.

Then, the single-crystalline Si thin film 220 is doped with an n-typeimpurity, to be converted to an n-type Si thin film, as shown in FIG.48. Thereafter a gate oxide film 228 and a gate electrode 230 areselectively formed on the upper surface of the n-type single-crystallinethin film 220. Further, these are employed as masks to selectively dopethe upper surface of the single-crystalline Si thin film 220 with ap-type impurity, thereby forming a drain layer 224 and a source layer226. Namely, these layers are formed by self alignment. Due to thisstep, the single-crystalline Si thin film 220 forms a p-channel MOStransistor.

Then, an insulating film 232 of SiO₂ or the like is formed over theentire upper surface. Then, desired portions of the insulating films 232and 212 are selectively etched to form an opening serving as a contacthole. Further, a conductive wiring layer 234 of aluminum, for example,is applied onto the overall upper surface of the insulating film 232including the contact hole, and thereafter the wiring layer 234 isselectively removed to couple the elements in a desired manner (FIG.50).

As hereinabove described, it is possible to selectively form asingle-crystalline layer on a desired specific region of the substrate202 in the method according to this preferred embodiment. Further, it ispossible to implement a device having a three-dimensional structure byforming a new element on the single-crystalline layer, since thesubstrate 202 itself is already provided with an element. In the methodaccording to this preferred embodiment, a single-crystalline thin filmcan be formed on the insulating film 212 of SiO₂, whereby the elementprovided in the substrate 202 can be easily isolated from a new elementprovided thereon in the three-dimensional device.

Further, it is also possible to form a plurality of new elements on thesubstrate 202, as shown in FIG. 51. At this time, two new elements (twop-channel MOS transistors in FIG. 51) are provided in single-crystallineSi thin films 220 which are formed independently of each other. Thus,these elements can be easily isolated with no provision of a LOCOS layeror an isolation layer. Consequently, steps of manufacturing the deviceare simplified and the degree of integration of the elements isimproved.

Although an n-type impurity is introduced into the selectively formedsingle-crystalline Si thin films 220 in the aforementioned preferredembodiment, the same may alternatively be introduced in the stage of theSi film 216, or into the overall surface of the Si film 214. In anymethod, it is possible to finally form the device of thethree-dimensional structure shown in FIG. 50 or 51.

<B-3. Fifteenth Preferred embodiment>

As hereinabove described, the Si film 214 (FIG. 45) is selectivelyremoved to form the Si film 216 (FIG. 46) and thereafter an Ne atomcurrent is applied (FIG. 47) to convert the same to thesingle-crystalline Si thin film 220 (FIG. 48). Alternatively, theoverall upper surface of the Si film 214 shown in FIG. 45 may beirradiated with the Ne atom current to be converted to asingle-crystalline thin film, so that the Si film 214 is thereafterselectively removed to form the single-crystalline Si thin film 220shown in FIG. 48. Subsequent steps are similar to those of thefourteenth preferred embodiment.

<B-4. Sixteenth Preferred embodiment>

As hereinabove described, the amorphous or polycrystalline Si film 214is previously formed (FIG. 45) and thereafter irradiated with the Neatom current, to be converted to a single-crystalline thin film in thefifteenth preferred embodiment. Alternatively, the apparatus 100 may beemployed after the step shown in FIG. 43 is completed to grow anamorphous Si thin film on the insulating film 212 while simultaneouslycarrying out application of an Ne atom current, thereby forming asingle-crystalline Si thin film on the insulating film 212. Thereafterthe single-crystalline Si thin film is selectively removed, to form thesingle-crystalline Si thin film 220 shown in FIG. 48. Subsequent stepsare similar to those of the fourteenth and fifteenth preferredembodiments.

<B-5. Seventeenth Preferred embodiment>

FIGS. 52 to 60 are process diagrams in relation to a method according toa seventeenth preferred embodiment. As shown in FIG. 52, an amorphous orpolycrystalline Si thin film is first formed on a substrate 502 which ismade of SiO₂, by CVD or the like. Thereafter the apparatus 100 isemployed to irradiate the Si thin film with an Ne atom current, therebyconverting the Si thin film to a single-crystalline Si thin film 504which is regulated in crystal orientation so that a (100) plane isexposed on the upper surface. Alternatively, the apparatus 101 may beemployed in place of the apparatus 100, to grow an amorphous Si thinfilm on the substrate 502 while irradiating the same with an Ne atomcurrent for forming the single-crystalline Si thin film 504.

Then, the upper surface of the single-crystalline Si thin film 504 isselectively thermally oxidized, to form LOCOS layers 506, as shown inFIG. 53. Thereafter p-type or n-type impurities are introduced into therespective ones of single-crystalline Si thin film regions 508, 510 and512 which are isolated from each other by the LOCOS layers 506, therebyconverting these single-crystalline Si thin film regions 508, 510 and512 to p-type or n-type semiconductor regions, as shown in FIG. 54.

Then, gate oxide films 514 and 515 of SiO₂ and gate electrodes 516 and517 of polycrystalline Si are formed on the upper surfaces of thesingle-crystalline Si thin film regions 512 and 510 respectively, asshown in FIG. 55. Thereafter these gate oxide films 514 and 515 and gateelectrodes 516 and 517 are used as masks to selectively introduce n-typeand p-type impurities into the single-crystalline Si thin film regions512 and 510 from the upper surfaces, as shown in FIG. 56. Consequently,source and drain layers are formed in the single-crystalline Si thinfilm regions 512 and 510 respectively.

Then, an insulating film 526 of SiO₂ is formed on an upper surfaceportion excluding the upper surface of the single-crystalline Si thinfilm region 508, as shown in FIG. 57. Thereafter the apparatus 101 isemployed to apply an Ne atom current from the upper surface, as shown inFIG. 58. At this time, only the single-crystalline Si thin film region508 which is not covered with the insulating film 526 of SiO, isselectively irradiated. Directions of irradiation are set in a pluralityof directions which are perpendicular to a plurality of densest planes(111) of single-crystalline Si which is so oriented that one (111) planeis exposed on the upper surface. Thus, the single-crystalline Si thinfilm region 508 is converted to a single-crystalline Si layer 530 whichis so regulated in crystal orientation that the (111) plane is exposedon the upper surface. Namely, the crystal orientation of thesingle-crystalline Si thin film region 508 is converted. The region 528which is masked with the insulating film 526 of SiO₂ and not subjectedto irradiation is a region to be provided with a CMOS element. On theother hand, the single-crystalline Si layer 530 which is converted incrystal orientation is provided with a pressure sensor, for example.Then, an insulating film 532 of SiO₂ is formed on the overall uppersurface, as shown in FIG. 59. This insulating film 532 includes theinsulating film 526. Thereafter a desired portion of the insulating film532 is selectively etched to form an opening for serving as a contacthole. Further, a conductive wiring layer 534 of aluminum, for example,is applied to the overall upper surface of the insulating film 532including the contact hole, and this wiring layer 534 is thereafterselectively removed to couple the elements in a desired manner (FIG.60).

Due to the aforementioned steps, a CMOS 528 and a pressure sensor 536are formed in the single-crystalline Si thin film 504 bysingle-crystalline Si materials having different crystal orientations ina parallel manner. The single-crystalline Si forming the CMOS 528 ispreferably oriented so that a (100) plane is along the major surface ofthe substrate, while the single-crystalline Si forming the pressuresensor is preferably oriented so that the (111) plane is along the majorsurface of the substrate. In the method according to this preferredembodiment, it is possible to form a composite device in which aplurality of elements having different preferable crystal orientationsare provided in the same single-crystalline Si thin film. In the methodaccording to this preferred embodiment, further, it is possible to forman element which is made from single-crystalline Si on the substrate 502of SiO₂, which is not a single crystal. Namely, this method has such anadvantage that the material for the substrate is not limited.

<B-6. Eighteenth Preferred embodiment>

As hereinabove described, an amorphous or polycrystalline Si thin filmis formed on the substrate 502 by CVD or the like and thereafter theoverall upper surface of this Si thin film is irradiated with an Ne atomcurrent so that the overall region thereof is converted to thesingle-crystalline Si thin film 504 which is so oriented that the (100)plane is exposed on the upper surface (FIG. 52). Alternatively, amasking material 540 having a prescribed masking pattern may be formedon an upper surface to be thereafter irradiated with an Ne atom current,so that only a region of an Si thin film to be provided with a CMOS isselectively irradiated with the Ne atom current, as shown in FIG. 61.Thus, only the region to be provided with a CMOS is converted to asingle-crystalline Si thin film 542 having an upper surface of a (100)plane, while another region 544 remains in the original state of theamorphous or polycrystalline Si thin film. Subsequent steps are similarto those of the seventeenth preferred embodiment.

The method according to the eighteenth preferred embodiment has aneffect similar to that of the seventeenth preferred embodiment. Namely,it is possible to form a composite device in which a plurality ofelements having different preferable crystal orientations are providedin the same single-crystalline Si thin film. Further, this preferredembodiment has such an advantage that the material for the substrate isnot limited, similarly to the seventeenth preferred embodiment.

<B-7. Nineteenth Preferred embodiment>

FIG. 62 is a front elevational view showing the structure of a sampleholder in an apparatus for forming a single-crystalline thin filmaccording to a nineteenth preferred embodiment of the present invention.This sample holder is assembled into the apparatus 100 in place of thesample holder 10. In this sample holder, a reflector 12 is fixed to afixed table 702 through supports 712. Further, a movable table 706 ishorizontally slidably supported by the fixed table 702. A seatingportion of this movable table 706 is fitted with a screw 708 which isrotated/driven by a motor 710, to be horizontally moved followingrotation of the screw 708. This seating portion is provided with ahorizontal driving mechanism (not shown) having a motor and a screwsimilarly to the fixed table 702, to horizontally drive an upper memberof the movable table 706. A direction for sliding the seating portion isperpendicular to that for sliding the upper member. A substrate 11 to beirradiated is placed on the upper member. This substrate 11 is locatedunder the reflector 12.

FIG. 63 is a plan view typically showing an operation of this sampleholder. The substrate 11 is relatively scanned with respect to thereflector 12 along two orthogonal directions by action of the twohorizontal driving mechanisms. Therefore, it is possible tohomogeneously irradiate the overall surface of the substrate 11, whichhas a wider area as compared with an opening of the reflector 12 servingas an opening for passing beams, with the beams.

When this sample stand is employed, it is possible to efficiently applythe beams by employing an apparatus 101a for forming asingle-crystalline thin film which comprises a magnetic lens 720, asshown in FIG. 64. The magnetic lens 720 is adapted to focus an ioncurrent which is downwardly sprayed from an ion source 2 into the formof a strip. FIG. 65 is a model diagram showing such a state that an ioncurrent is focused by the magnetic lens 720. Due to the action of themagnetic lens 720, the ion current has a strip-type sectional shape inthe vicinity of the reflector 12f. Therefore, the reflector 12f also hasa shape along this strip. Similarly to those in the apparatuses 100 and101, the ion current is substantially converted to a neutral atomcurrent in the vicinity of the reflector 12f. The substrate 11 isirradiated with components 726 of the atom current reflected from thereflector 12f and directly incident components 724. The angle ofinclination of the reflector 12f is so adjusted that directions ofincidence of these two components are orthogonal to a plurality ofdensest planes of a single-crystalline thin film to be formedrespectively.

It is possible to efficiently irradiate a wide region on the substrate11 in single scanning, by scanning the substrate 11 in a direction 728which is perpendicular to the "strip of the atom current". Therefore, itis possible to attain irradiation of the substrate 11 having a wide areain a small number of scanning times. In other words, it is possible toform a single-crystalline thin film with higher efficiency by employingthe apparatus 101a. This is particularly effective when the width of thesubstrate 11 is shorter than a major axis width of the "strip of theatom current". At this time, the substrate 11 may simply be scannedalong one direction 728, whereby a single-crystalline thin film can befurther efficiently formed. Further, the driving mechanism provided inthe sample holder is sufficiently implemented only by a single drivingmechanism which is integrated in the fixed table 702, whereby the sampleholder is simplified in structure.

<B-8. Twentieth Preferred embodiment>

FIG. 66 is a front elevational view typically showing the structure of areflector support which is provided in an apparatus for forming asingle-crystalline thin film according to a twentieth preferredembodiment of the present invention. This reflector support rotatablysupports an end of a reflector 802 by a hinge 804, while rotatablysupporting another end by another hinge 806 which is provided on theforward end of a connecting bar 808. The connecting bar 808 is axiallydriven by a piston 810. Following the axial movement of the connectingbar 808, the reflector 802 is rotated about the hinge 804. Consequently,an angle θ of inclination of a reflecting surface is changed in thereflector 802. Namely, the angle of inclination is variable in thereflecting surface of the reflector 802 provided in this apparatus.Thus, it is possible to form single-crystalline thin films havingvarious crystal orientations and crystal structures by employing asingle apparatus. Namely, formation of various types ofsingle-crystalline thin films can be economically attained.

Further, it is possible to efficiently form various types ofsingle-crystalline thin films on a single substrate 11. This is becausevarious types of single-crystalline thin films can be formed whileinserting the substrate 11 in the apparatus. It is possible toinstantaneously set a prescribed angle of inclination by controlling theoperation of the piston 810 by a computer.

<B-9. Twenty-first Preferred embodiment>

FIG. 67 is a plan view typically showing the structure of a reflectorsupport 902 which is provided in an apparatus for forming asingle-crystalline thin film according to a twenty-first preferredembodiment of the present invention. This reflector support 902comprises a plurality of arms 904 which are rotated/driven aboutvertical axes. Each one of a plurality of reflectors 906a to 906f, whichare different from each other, is mounted on a forward end portion ofeach arm 904. The plurality of reflectors 906a to 906f are so formedthat numbers or angles of incidence of atom current components which areincident upon a substrate 11 are different from each other. Namely, thereflectors 906a to 906f are different from each other in numbers ofreflecting surfaces and angles of inclination. Since the arms 904 arerotated/driven, it is possible to arbitrarily select a desired reflectorto be set in an irradiated region 908 which is irradiated with the atomcurrent from the plurality of types of reflectors 906a to 906f.

Therefore, it is possible to form single-crystalline thin films havingvarious crystal orientations and crystal structures only by a singleapparatus, similarly to the apparatus according to the twentiethpreferred embodiment. Namely, it is possible to economically formvarious types of single-crystalline thin films. Further, it is possibleto efficiently form various types of single-crystalline thin films on asingle substrate 11.

<B-10. Twenty-second Preferred embodiment>

The reflector(s) and the reflector support provided in each of thenineteenth to twenty-first preferred embodiments can also be employed inthe apparatus 101, in place of the apparatus 100. Namely, thereflector(s) and the reflector support can be applied to both of anapparatus for forming an amorphous or polycrystalline thin film andthereafter converting the same to a single-crystalline film and anapparatus for simultaneously carrying out these operations.

<B-11. Twenty-third Preferred embodiment>

FIG. 68 is a plan view typically showing the structure of an apparatusfor forming a single-crystalline thin film according to a twenty-thirdpreferred embodiment of the present invention. In this apparatus, anetching unit portion 1104 for etching a substrate 11, a film formingunit portion 1106 for forming an amorphous or polycrystalline thin filmon the substrate 11, and an irradiation unit portion 1108 forirradiating the substrate 11 with an atom current are arranged around acarrier chamber 1102. Further, treatment chambers for storing thesubstrate 11 in the respective unit portions 1104, 1106 and 1108communicate with each other through the carrier chamber 1102. Thecarrier chamber 1102 is provided with an inlet 1110 and an outlet 1112for receiving and discharging the substrate 11 respectively. Both of theinlet 1110 and the outlet 1112 are provided with airtight switchabledoors (not shown). The carrier chamber 1112 is provided with a carrierrobot 1114, which receives and discharges the substrate 11 whileautomatically inserting and extracting the same into and from therespective treatment chambers.

In the apparatus according to this preferred embodiment, the respectivetreatment chambers communicate with each other, whereby it is possibleto immediately start formation of a thin film after carrying out etchingfor removing an oxide film before forming a thin film on the substrate11 while preventing new progress of oxidation. Thus, it is possible toreliably form a thin film having excellent and homogeneouscharacteristics while efficiently carrying out respective treatments.Further, it is possible to efficiently carry the substrate 11 into therespective treatment chambers due to provision of the carrier robot1114.

<B-12. Twenty-fourth Preferred embodiment>

FIG. 69 is a front sectional view typically showing the structure of anapparatus for forming a single-crystalline thin film according to atwenty-fourth preferred embodiment of the present invention. Thisapparatus comprises two ECR ion sources 1204a and 1204b, in place of thereflector 12. Namely, atom currents which are supplied from the ECR ionsources 1204a and 1204b are directly incident upon the upper surface ofa substrate 11. These ECR ion sources 1204a and 1204b are set to haveprescribed angles with respect to the major surface of the substrate 11.Consequently, the atom currents are incident upon the upper surface ofthe substrate 11 in directions of incidence which are perpendicular to aplurality of densest planes of a single-crystalline thin film to beformed. It is possible to form a single-crystalline thin film on thesubstrate 11 also by employing such an apparatus having a plurality ofbeam sources, in place of the apparatus 100 comprising the reflector 12.

In this apparatus, a mechanism for adjusting the attitude of thesubstrate 11 is further added to a sample holder 1208 which is set in atreatment chamber 1202. Namely, the sample holder 1208 is rotatable in ahorizontal plane, whereby it is possible to rotate the substrate 11 fordirecting an orientation flat 11a, which may be provided in thesubstrate 11, to a prescribed direction. When the substrate 11 which isplaced on a carrier unit 1206 is carried through an inlet 1204 providedon a side surface of the treatment chamber 1202 of this apparatus andplaced on the sample holder 1208, optical means detects the direction ofthe orientation flat 11a and the sample holder 1208 is rotated by aprescribed amount in order to correct the direction to a prescribed one.The amount of rotation is calculated by a control unit part (not shown)storing a computer therein.

The direction of the orientation flat 11a generally has a constantrelation to the crystal orientation of a single-crystalline layerforming the substrate 11. Therefore, it is possible to set the crystalorientation of the single-crystalline layer forming the substrate 11 andthat of a single-crystalline thin film to be newly formed thereonregularly in a desired relation by setting the orientation flat 11a in aprescribed direction. Thus, it is also possible to epitaxially form anew single-crystalline thin film on the single-crystalline layer formingthe substrate 11, for example, by employing this apparatus.

FIG. 70 is a front sectional view typically showing the structure ofanother apparatus for forming a single-crystalline thin film accordingto the twenty-fourth preferred embodiment of the present invention. Alsoin this apparatus, it is possible to horizontally rotate a substrate 11to adjust its attitude. Namely, a sample holder 1208 can be horizontallyrotated by a rotation driving part 1214. This apparatus furthercomprises a crystal orientation detecting unit portion 1210 fordetecting the crystal orientation of the substrate 11 having asingle-crystalline structure. The crystal orientation detecting unitportion 1210 has a function of irradiating the surface of the substrate11 with X-rays, for example, and catching a diffraction image thereof.An electric signal expressing the diffraction image obtained by thecrystal orientation detecting unit portion 1210 is transmitted to acontrol part 1212 storing a computer therein. The control part 1212decodes the diffraction image from this signal to calculate the crystalorientation in the substrate 11 while calculating difference between thesame and a desired crystal orientation, and instructs an angle ofrotation for correcting the orientation to the rotation driving part1214. The rotation driving part 1214 rotates the sample holder 1208along the instruction. The aforementioned operation eliminates thedifference, to regularly set the crystal orientation of thesingle-crystalline layer forming the substrate 11 and that of thesingle-crystalline thin film to be newly formed thereon in a desiredrelation.

The apparatus shown in FIG. 70 has such an advantage that the crystalorientation can be adjusted with respect to an arbitrarysingle-crystalline substrate having no orientation flat 11a,dissimilarly to the apparatus shown in FIG. 69. Considering that therelation between the crystal orientation of the substrate 11 and thedirection of the orientation flat 11a is not accurate in general, it canbe said that the apparatus shown in FIG. 70 can adjust the crystalorientation in higher accuracy as compared with the apparatus shown inFIG. 69.

<B-13. Twenty-fifth Preferred embodiment>

FIG. 71 is a partially fragmented front elevational view typicallyshowing a sample holder which is provided in an apparatus for forming asingle-crystalline thin film according to a twenty-fifth preferredembodiment of the present invention. This sample holder is employedalong with the apparatus 101. Namely, this sample holder is employed inan apparatus for growing an amorphous or polycrystalline thin film bysupplying a reaction gas onto a substrate 11 while irradiating the samewith an atom current. In this sample holder, a reflector 12 is fixedlysupported on a fixed table 1302 through a support 1304. A rotatabletable 1306 for receiving the substrate 11 is connected with a rotaryshaft 1308, which is rotated/driven by an rotation/driving unit portion(not shown) thereby rotating the rotatable table 1306. Upon suchrotation of the rotatable table 1306, the substrate 11 which is placedthereon is rotated. It is possible to eliminate inhomogeneity appearingin the thickness of the as-grown thin film due to inhomogeneity in areaction system, i.e., inhomogeneity in distribution of a reaction gasonto the substrate 11 or that in temperature distribution on thesubstrate 11 by rotating the substrate 11 and properly changing itsdirection. On the other hand, relative positions of the reflector 12 andthe substrate 11 are changed upon rotation of the substrate 11. Whenthis sample holder is employed, therefore, application of the atomcurrent is intermittently carried out so that the direction of thesubstrate 11 is changed to carry out only growth of a thin film, i.e.,only film formation, with limitation to irradiation pauses. Further, thedirection of the substrate 11 is returned to the original one beforenext irradiation is started. These operations are repeated to carry outfilm formation and conversion to a single crystal.

FIG. 72 is a plan view typically showing another example of the sampleholder. This sample holder is adapted to implement treatment of thesubstrate 11 in a batch processing system, and employed in combinationwith the apparatus 100. In this sample holder, substrates 11 to betreated are placed on peripheral portions of a rotary shaft of arotatable table 1310. FIG. 72 illustrates such an example that foursubstrates 11 are placed. Among these substrates 11, only that providedin a position of "A" in FIG. 72, for example, is irradiated with an atomcurrent. A reaction gas is supplied in all positions "A" to "D".

When the rotatable table 1310 is intermittently rotated, the substrate11 occupying the position "A" is subjected to both of irradiation andsupply of the reaction gas. Namely, film formation and singlecrystallization progress at the same time. In the respective ones of theremaining positions "B" to "D", only supply of the reaction gas iscarried out with progress of only film formation. Further, thedirections of the substrates 11 are varied with the positions "A" to"D". When the substrates 11 successively itinerant the positions "A" to"D", therefore, it is possible to eliminate inhomogeneity in degree offilm formation caused by inhomogeneity in a reaction system. Namely, itis possible to form a single-crystalline thin film having a uniformthickness on each substrate 11 also by employing this sample holder.Further, it is possible to regularly carry out irradiation with an atomcurrent in the position "A". Therefore, it is possible to furtherefficiently form a single-crystalline thin film as compared with a caseof employing the sample holder shown in FIG. 71.

<B-14. Twenty-sixth Preferred embodiment>

FIG. 73 is a front sectional view typically showing a sample holderwhich is provided in an apparatus for forming a single-crystalline thinfilm according to a twenty-sixth preferred embodiment of the presentinvention. In this sample holder, a reaction gas supply member 1412defining a reaction gas supply path in its interior is rotatably mountedon a bottom portion of a treatment vessel 1402 while maintaining anairtight state. Therefore, this sample holder is suitably integrated inthe apparatus 100 having no separate reaction gas supply system.

This reaction gas supply member 1412 is rotated/driven by a belt 1428.The reaction gas supply member 1412 is in a three layer structureprovided with an inner pipe 1416 which is located on the innermostlayer, an outer pipe 1414 which is located on the outermost layer, andan intermediate pipe 1418 which is located on the intermediate layer.Thus, the reaction gas supply member 1412 defines a supply path and anexhaust path for a reaction gas between the respective layers. Further,a reaction gas supply port 1420 and a reaction gas discharge port 1426are rotatably coupled to the reaction gas supply member 1412 throughrotary seals 1430 and 1432 for maintaining airtightness respectively.

In addition, a support 1406 for fixedly supporting a sample fixing table1404 is inserted in the interior of the reaction gas supply member 1412.A substrate 11 serving as a sample is placed on the sample fixing table1404, while a heater 1408 for heating the sample is provided on a bottomsurface of the sample fixing table 1404. This heater 1408 may be rotatedat need, in order to improve temperature distribution on the substrate11. The sample fixing table 1404 is so fixed that the same is notrotated following rotation of the reaction gas supply member 1412.

A reaction gas which is supplied from the reaction gas supply port 1420passes through the supply path defined between the intermediate pipe1418 and the inner pipe 1416, to be sprayed toward the upper surface ofthe substrate 11 from a reaction gas spray port 1422. A reacted residualgas enters another path which is defined between the outer pipe 1414 andthe intermediate pipe 1417, i.e., the exhaust path from a reaction gascollection port 1424, and further passes this exhaust path to bedischarged to the exterior from the reaction gas discharge port 1426. Itis possible to homogeneously grow a prescribed thin film on thesubstrate 11 by rotating the reaction gas supply member 1412. Further,it is possible to continue the growth without interrupting irradiationwith an atom current, since the substrate 11 is not rotated. Namely, itis possible to homogeneously form a film without interrupting singlecrystallization caused by irradiation with an atom current in thissample holder. Thus, it is possible to further efficiently form asingle-crystalline thin film of a uniform thickness on the substrate 11.

<B-15. Twenty-seventh Preferred embodiment>

FIG. 74 is a front sectional view typically showing the structure of anapparatus for forming a single-crystalline thin film according to atwenty-seventh preferred embodiment of the present invention. Thisapparatus comprises two ECR ion sources 1204a and 1204b, similarly tothe apparatus shown in FIG. 69. The feature of the apparatus accordingto this preferred embodiment resides in provision of control unitportions 1502 and 1504 for independently adjusting density levels of ionbeams generated from the two ECR ion sources 1204a and 1204b. Thesecontrol unit portions 1502 and 1504 separately, i.e., independentlycontrol the outputs of the two ECR ion sources 1204a and 1204b, wherebyit is possible to easily optimize density levels of the ion beamssupplied from the same. Thus, it is possible to stably form ahigh-quality single-crystalline thin film on the substrate 11.

<B-16. Twenty-eighth Preferred embodiment>

FIG. 75 is a front sectional view typically showing the structure of anapparatus for forming a single-crystalline thin film according to atwenty-eighth preferred embodiment of the present invention. Thisapparatus also comprises two ECR ion sources 1204a and 1204b, similarlyto the apparatus shown in FIG. 74. The feature of the apparatusaccording to this preferred embodiment resides in that a bias voltage isapplied across the two ECR ion sources 1204a and 1204b and a substrate11, in a direction for accelerating ions. Namely, a dc voltage supplycircuit is interposed in parallel in a series circuit of an RF powersource 1602 for generating a high frequency and a matching circuit 1604for ensuring impedance matching, i.e., a circuit for supplying a highfrequency to the ECR ion sources 1204a and 1204b. The dc voltage supplycircuit is formed by a series circuit of a dc power source 1606 and aninductor 1608 for blocking a high frequency.

Supply of the high frequency and that of the dc voltage are allotted tothe two ECR ion sources 1204a and 1204b by time sharing through actionof a switching relay 1610. These are alternately supplied to the two ECRion sources 1204a and 1204b by time sharing, in order to preventdisturbance of a normal flow of an ion current caused by interference ofdc voltages applied thereto.

In the apparatus according to this preferred embodiment, a bias voltageis applied across the ECR ion sources 1204a and 1204b and the substrate11 in a direction for accelerating ions, whereby the atom current isadvantageously improved in directivity. A similar effect is attainedalso when the bias voltage is simultaneously supplied to the two ECR ionsources 1204a and 1204b in place of the alternate supply by timesharing. Alternatively, two dc voltage supply circuits may be providedto independently supply bias voltages to the two ECR ion sources 1204aand 1204b respectively. In this case, it is possible to apply optimumbias voltages to the respective ECR ion sources 1204a and 1204b, wherebyoptimum irradiation conditions can be obtained.

<B-17. Twenty-ninth Preferred embodiment>

FIG. 76 is a front sectional view typically showing the structure of anapparatus for forming a single-crystalline thin film according to atwenty-ninth preferred embodiment of the present invention. Thisapparatus also comprises two ECR ion sources 1204a and 1204b, similarlyto the apparatus shown in FIG. 75. The feature of the apparatusaccording to this preferred embodiment resides in that grids 1702 and1704 to which bias voltages for adjusting ion extracting conditions areapplied are provided in the vicinity of ion outlet ports of the two ECRion sources 1204a and 1204b. Dc power sources 1706 and 1708 areinterposed between the grids 1702 and 1704 and a substrate 11respectively. The two grids 1702 and 1704 are separated from each other,so that the voltages applied thereto can be adjusted independently ofeach other.

When bias voltages are applied across the grids 1702 and 1704 and thesubstrate 11 in directions for accelerating ions, for example, an atomcurrent is improved in directivity. In this apparatus, further, thelevels of the bias voltages which are applied to the two grids 1702 and1704 can be adjusted independently of each other, whereby it is possibleto apply optimum bias voltages in response to operating states of thetwo ECR ion sources 1204a and 1204b. Thus, it is possible to efficientlyform a high-quality single-crystalline thin film on the substrate 11.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A beam irradiating method of irradiating a targetsurface of a sample with a gas beam, said method comprising the stepsof:setting said sample in a container; and irradiating said targetsurface of said sample being set in said container with said gas beam atan energy lower than a threshold energy of sputtering in a surface of aportion being irradiated with said gas beam along an inner wall of saidcontainer.
 2. The method according to claim 1, further comprising thestep of:separating said gas beam into a plurality of components with areflector, and wherein a surface portion of said reflector is irradiatedby said gas beam and the energy of said gas beam is lower than athreshold energy of sputtering in said surface portion of saidreflector.
 3. The method according to claim 1, further comprising thestep of:holding said sample in said container with a sample holder,wherein a surface portion of said sample holder is irradiated by saidgas beam and the energy of said gas beam is lower than a thresholdenergy of sputtering in said surface portion of said sample holder. 4.The method according to claim 3 wherein the sample holder is made of Ta,W, or Pt.
 5. The method according to claim 1 wherein the energy of saidgas beam is lower than the threshold energy of sputtering of Si.